SQL Data Compare is filling up the disk
The software uses the Windows API to get a temporary file name. These temporary files go into a directory pointed to by your %TMP% user environment variable. If you go to your system properties from the Control Panel, click the Advanced tab, then Environment variables, you can view or change the folder where all of the temp files go.
The temporary files should get cleaned out at the end of the session, but they do not if you cancel a data comparison part-way through or there is an error in comparing.