Linda & Russ, I have had the same problem since I first installed the software.
Linda, It probably seems like I have nothing to offer to help you, but perhaps if I share info with Russ, he might be able to figure out what's going on with both of us!
I am running Windows Vista SP2.I have FTM2012.99% of the time, I make changes to the website, then sync the new info into FTM.I have 7000+ people & 1000+ media files, I have no idea how many citations I have, but a whole lot of them.
In addition to the problems Linda has described, I add the following:
When I open FTM, sometimes it freezes for a very long time.I open up Task Manager, & FTM *always* uses around 500,000k memory, making it impossible for me to leave open any other programs if I hope to get a successful sync at all.Also, I have to right-click & run as administrator to get it past the 'connecting to server' portion of the sync.
When it finally finishes it's initial start-up, & I open my tree (it's set to automatically sync, btw) it always opens to the people tab.I have to click on the plan tab, the select Sync Now.It seems to progress through the syncing from the website to FTM, but then it says it's uploading changes from the FTM to the website (which I've only made changes to FTM twice since I've had it), the top bar stops progressing, & the bottom bar turns from a solid green progress bar to a what I can only describe as about a 1 inch soft or blurry edged lighter green section that runs the length of the total bar for up to 10 minutes before I get the Sync Error message that Linda mentions.
I have compacted the file several times, uninstalled (including the manual uninstall instructions provided in the website FAQ/Help Center), & have now reluctantly accepted the fact that I have to unlink & redownload from Ancestry.com every time I make a change if I want a copy on my computer.
I think that's everything, but if I've forgotten something, I'll be sure to add it.