Before posting, please read how to report bug or request support effectively.
Bug reports without an attached log file are usually useless.
:diff - Starts the external diff program specified in the TortoiseSVN settings. The /path specifies the first file. If the option /path2 is set, then the diff program is started with those two files. If /path2 is omitted, then the diff is done between the file in /path and its BASE. To explicitly set the revision numbers use /startrev:xxx and /endrev:xxx. If /blame is set and /path2 is not set, then the diff is done by first blaming the files with the given revisions.