Error during file transfers to a local (LAN) SMB share while Dropbox client is running (0x8007003B)

[Rocinante]

Hello everyone,

I've been using Dropbox (version 114.4.426) on two PCs and 3 notebooks at home (for different family members; no pro user yet), for about several years now. I just recently discovered a problem with one of the notebooks (Lenovo IdeaPad S340-15IWL running Windows 10 64 Bit, 20H2):

When I copy a large file (>1GB, did not test with smaller files) to a SMB share in my LAN, I get a "0x8007003B - Unexpected network error" after some minutes (time of occurrence always different).

Since I got no problems on the other machines (same Windows versions, same LAN), I did a lot of testing: network hardware, router, network-cables, network configuration, SMB configuration and so on. I could not reproduce the problem on any machine except for that one notebook.

Things I tested along the journey (only some examples):

• Ran file transfer tests with different sizes, ranging from 1 GB to 30 GB
• Changed network hardware: router, cables
• Always checked the other machines (PC and notebooks), running the same tests, where the file transfers always succeeded
• Checked file/transfer/user permissions
• Updated all drivers, BIOS and windows
• Deactivated firewall (there are no third party firewalls installed, or other virus or malware scanners)
• Ran tests via LAN and WLAN
• Run via safe mode, closed all unnecessary services and background programs
• Changed different network settings, like MTU sizes

There were other tests and the whole testing took me about a full week.

Now some of you might ask the (justified) question why I'm coming to the Dropbox forums for this:

After hours and hours trying to find the cause of the "0x8007003B - Unexpected network error", it all came down to the Dropbox client: As soon as I close the Dropbox client on that notebook, every single file transfer succeeds, no problem at all, for all of my tests (note that during the tests, Dropbox did not sync any files). The moment I started the Dropbox client again, every single file transfer test showed the network error and aborted file transfers.

So from all my tests, the Dropbox client is the only application that causes the file transfer to fail ("0x8007003B - Unexpected network error", and only on that single notebook), which is 100% reproducible.

(As you certainly guessed, my workaround is currently to close Dropbox when I transfer large files. But this isn't a real solution, because there are some background tasks that periodically transfer a decent amount of data, like automatic backups.)

Long story short, does anyone have any idea, why the problem occurs when Dropbox is running?

I really appreciate your help, thanks a lot!

Kind regards,
Ben

[Lusil]

Hey @Rocinante, thanks for reaching out to us, and awesome work with the troubleshooting!

Generally, the error message that you're seeing is Windows-based. 

However, since it comes up when the desktop app is running, could you let me know if the app was installed with admin privileges? 

Give me a shout whenever you have a moment to check this out, thanks!

[Rocinante]

Hey @Lusil,

thanks a lot for your answer!

I'm using a windows user account with admin rights. When I install the Dropbox client (desktop app), Windows asks for permissions (the Windows UAC - User Account Control), so I don't think missing admin rights might be a problem.

But to be absolutely sure, I will uninstall and reinstall Dropbox with admin rights when I come home today (in about 5 hours) and report back.

[Lusil]

No worries, @Rocinante. Give me a shout whenever you have any updates and I'll make sure to get back to you as soon as possible.

Thanks again!

[Rocinante]

Hello @Lusil,

sorry for the late answer, I was reinstalling the Dropbox client and made sure to have admin rights (windows administraor) and then I ran all of my tests again, which took some time.

The first runs were promising - but after about 6 file transfers, the error popped up again. I checked again that the file transfer works without the Dropbox client running in the background, and it does.

To better demonstrate the problem, I compiled a small video of the problem with some text in it, so its easier to understand what I'm doing. Please, have a look:

• https://www.dropbox.com/s/rccnbqeaz2hbm7a/2021-02-05_dropbox-problem.mp4?dl=0

I'm doing 3 file transfers - the first one with Dropbox running, which fails. The second one without Dropbox, which succeeds. And, just to be sure, starting the Dropbox client again and the file transfer fails again.

(The network is really simple: [Notebook] <---> [Router/Switch] <---> [RaspPI with NAS share])

Do you have any ideas what tests I could also run? I'm really at the end of my ideas, to be honest 

[Lusil]

From your description, it looks like you have set it up with a NAS, which isn't currently a supported location for the Dropbox folder.

This is due to it generally not working well in being able to sync changes made to the files within the account.

You can find more information about this in Walter's post, here. 

Have a look through and let me know if you have any other questions or issues along the way.

[Rocinante]

Hello @Lusil,

> From your description, it looks like you have set it up with a NAS, which isn't currently a supported location for the Dropbox folder.

no no, you misunderstood - maybe I did not describe it well enough.

My NAS has nothing to do with the Dropbox sync location. These are two separate things. I copy over a large file to my NAS via SMB, but when the Dropbox client is running, the network transfer fails - please see my video.

I did not configure Dropbox to sync to a NAS folder. Dropbox syncs to a normal local folder, complete independent of any of the shown file locations in the video.

This is the actual weird thing I try to describe here: As soon as the Dropbox client runs in the background, network file transfers to a NAS via SMB fail. As if Dropbox manipulates network settings or does other things in the background which cause a transfer of big files in the LAN to fail.

Or in other words: If I copy over a large file to my NAS, Dropbox does nothing, it just idles in the background.

Again: My NAS and Dropbox are complete separate.

[Jay]

Hi @Rocinante, just for clarification is that device the only machine running the Dropbox desktop application?

Additionally, when you installed with admin permissions, can you confirm you didn't right click the installer and then 'Run as administrator'? 

[Rocinante]

Hi @Jay,

---

@Jay wrote:
Hi @Rocinante, just for clarification is that device the only machine running the Dropbox desktop application?

---

no, as I said in the very first post, we have 2 PCs and 3 notebooks at home, all running the Dropbox client with basic accounts (no pro accounts). All are running version 115.4.601 (I updated since my first post). All are running Windows 10 and are up to date.

Furthermore, all of those machines transfer data to the same SMB share (backup and other date), all are on the same network - some via LAN, some via Wifi.

No machine has a problem except that one notebook.

---

@Jay wrote:
Additionally, when you installed with admin permissions, can you confirm you didn't right click the installer and then 'Run as administrator'? 

---

No, I can't confirm that to be honest. I in fact did right click the installer and chose "run as admin".

But, the user under which I installed the Dropbox client is administrator:

The user is also member of the local user group "Administrators".

(And it is the only user on the notebook.)

Isn't that enough? Is there a better way to install Dropbox, being "even more administrator"? 😉

Yesterday I ran a few more tests, but everytime it comes down to the Dropbox client, where my file transfers to the local SMB share only work when Dropbox is not running.

I appreciate any help, I'm really lost here...

[Jay]

Running the installer as admin isn't the method we recommend, as per the article my colleague linked.

As you mentioned you're not on a paid plan, if you don't have more than 3 devices connected, could you try an advanced reinstall of the app using the steps in this link?