The TABLEDIFF.exe utility can fail when it finds differences while comparing tables that have a DATETIME column as (part of) the primary key and the Regional Settings on the computer are not set to English (in my case, it is set to Dutch).
This seems to be caused by the fact that a date like 2012-11-17 is rendered as 11/17/2012 in English and as 17-11-2012 in Dutch. When it tries to insert this date into the comparison table that tablediff creates, it apparently incorrectly uses the regional format that gets rendered into the text file, and the insert fails.
When it compares these kind of dates and finds no differences, there is no issue and
Tablediff works as expected.
I've seen this happen on SQL Server 2008 R2 and 2012 both.