What xp-night said sort of interested me:
Then when u goto use lastrep to report it it says "you don't have permission to open this file. contact the file owned or an administrator to obtain permission"
Anyone who's getting this a lot, try the following as an experiment. After every single game (successful or not) delete or rename LastReplay.rep and report here if anything unusual happens (e.g. permission denied or something). The next time you get the error in SC, check the status of lastreplay, whether it exists and whether you can access/copy/rename it.