Cant establish secure internet connection

Hey there alhembd - how are you today?

From what I understand, you must be getting the error "Can't establish secure internet connection" on your desktop application. This can be usually caused by an antivirus, firewall, security program, proxy or VPN configuration blocking the Dropbox desktop client as all connections to the Dropbox service are done using a secure connection (SSL).

Since you get a "Cannot establish a secure connection" error, I would highly recommend to check all of the following:

1. Is your system incorrect?

Your computer will compare your system date to the expiration date of our SSL certificate. If your system time is stuck in the past or so far in the future that it’s outside of Dropbox's SSL certificate expiration date, a secure connection can’t be established and to correct this, you'll need to change your system time to the current date (either on your computer, your router, or both); just note that your OS time is different than the date/time that appears in the system tray or menu bar of your computer. 

2. Do you have a proxy or firewall blocking the Dropbox service?

• Dropbox uses standard internet ports (80 and 443) to transfer data. Regardless, many firewalls and security software (such as antivirus programs) will proactively block unauthorized/unknown internet services. If that's the case, you should add Dropbox to your proxy or firewall settings as an exception to connect to the Dropbox service.
• Known issues with ESET Endpoint Security Solutions: According to ESET's website, this product currently has a conflict with Dropbox when SSL scanning is enabled. Possible workarounds are to exclude the Dropbox certificate within the "Ask about non-visited sites" mode, as well as to exclude dropbox.exe from protocol filtering.
• Known issues with Kaspersky Endpoint Security 8: This product currently has a conflict with Dropbox that prevents users from connecting after the application is updated. The current workaround is to add an exclusion in Kaspersky to allow Dropbox to connect. The second option is to upgrade the application to the Kaspersky Endpoint Security 10 version. More information on Kaspersky's site.
• Known issues with HitmanPro (anti-malware): This product currently has a conflict with Dropbox that can block Dropbox sync operations. There are no known workarounds for this, however you can temporarily disable HitmanPro when you'd like to sync your Dropbox. Visit the HitmanPro website to learn more about the product, or to report false positives.

3. Are your default proxy settings incorrect?

Some external software programs will change your computer's default proxy settings when installed and may not alert you of this. Confirm that your proxy settings haven't changed and, if you don't use a proxy setting, select the option for "No proxy."  You can also use the Dropbox Preferences menu to set Proxy settings:

1. Click the Dropbox icon in the menu bar.
2. Select Preferences…
3. Click the Network tab.
4. Fill in your proxy settings under the section appropriately labeled Proxy Settings.

I hope this information helps and please let me know what you find!