It seems like Remaining Work is a required field. I guess, it is required in TFS and currently you have items which have remaining work empty and they are not valid. When they are not valid in tfs they could not be updated by teampulse sync. Could you try open the tfs item for one of the item you receive error in tfs and make some change manually. Usually, tfs shows error validation messages.
It would also be very helpful if you could send us the log files from the TeamPulse server. You can just zip up the Logs folder and attach it to your response. This folder is usually located here: C:\Program Files (x86)\Telerik\TeamPulse\Logs.