Started seeing exactly the same error 3 days ago, 2/27/2013. Still happening this morning 3/1. My last successful sync was 2/22, early evening CST. Using latest updates for FTM 2012 on Windows 7 SP1.
I tend to agree with other comments, appears to rooted in issues with the ancestry.com servers - not necessarily an issue with FTM.
I too have a lot of changes to sync - all made online, and I am hesistant to make more until this issue is resolved.
Does ancestry.com monitor this forum? An acknowledgement that they are aware of the issue and are working on a resolution would be reassuring.