Re: I Can't watch replays
No. stderr.txt is just where some error/debug-ish messages end up, so if it there was anything in it, it could give some hint as to what the problem might be (eg, if you make a .rpl file yourself, throw some random text into it and try'n load it, stderr.txt will probably say something about how parsing the thing went wrong). You checked stderr.txt right after trying to load a replay that didn't work and then quitting the game?
Did you check some non-working replays in notepad? I don't think stderr.txt will say anything if a replay-file is completely empty...