I am having this problem as well. It started sometime on Sunday or Monday.
I can login fine to Endnote Web, but when I try to get Endnote x6 to Sync, it is unable to do so. I have downloaded and installed the most recent version of Endnote.
When I click on the red exclaimation point, after “Sync Errors” it says “server.invalidRequest”
Any help on this from anyone?
I should also state that I am using Windows XP one one computer and Windows 7 on another.