Can't upload files due to "insufficient space"

I received an email that said the following: 

'Your Dropbox is no longer syncing because it's full. That means we can't back up new files you add to your Dropbox or sync to your other devices.

To get your Dropbox back to shape, upgrade to Dropbox Pro and get 1 TB (1,000 GB) of space, plus powerful sharing features.'

I already have Dropbox Pro - why am I getting this message? I have only used 30.5 GB out of 1.01 TB

Rich,

Here's the exact message: The item “Craig slide scans” can’t be copied because there isn’t enough free space.

@Craig: That's referring to the space on your hard drive.

@Elisabeth: It could be a fake email. Log in to the Dropbox website (don't use the links in the email, to be safe) and check your usage on the Account page.

Thanks, that is what I did. will delete email! :-}