I can confirm that this is a problem with 7.1.0_GA_3140.FOSS.
I have a customer with thirty people now accessing Zimbra. Two of them, in the same office, are having the UID issue.
One is Outlook 2010, the other is Outlook 2003. Both keep reporting the error. Here's an example.
MsgSeqNum 108, New UID 8404. Prev UID: 8404, Next UID: 0.
Server: mail.<domain name>.net
Error Code: 0x800CCCDC
As you can see, the 'Next UID:' seems to always be zero.
The 'microsoft answer' of 'it's the server problem, but delete your profile and recreate it' didn't fix this issue on either computer. (both deleting the IMAP account, and deleting the entire profile). In fact, it came back as soon as the next new email came in.
The Office 2010 machine is running Trend Micro Titanium, on Windows 7 Professional. The Office 2003 PC is running ClamAV for windows, with an Outlook plugin, on XP Professional. (115 megabytes of memory use just for the plugin. Sheesh). Trend Micro Titanium does not appear to have an active 'add-in' in Outlook 2010.
To reproduce the problem in Outlook 2010, I simply wait for the next email, or hit F9 and watch the "synchronizing subscribed folders for ..." for a bit. This is a slow process. (several minutes) and is terminated by the UID error.
The customer is NOT happy with Zimbra right now.