help with megui error plz

[runLoganrun]

Hi,
I attached log file from error. Hopefully someone can tell me what I'm doing wrong....
I should start by saying that I'm attempting to use MeGUI in WHS, in an effort to free up my computer....
Everything installed fine though, including Haali and FFDshow, and appears to work well, that remains to be seen I guess, with one strange exception- when I right click a file in cue and "load" to megui, it doesn't work??
Anyway I've had similar prob in Windows too, and can't figure out what I keep doing wrong, it's something to do with naming output vid file, and/or using mkv as source and output, I believe.
Should I just be encoding to mp4 from mkv source, and then remuxing with audio to mkv?
I've gotten one error a few times, which I think is what happened here, sorry can't remember exactly, but when it gets to 2nd pass it asked me "file..... exists already, would you like to overwrite?" I believe in this case I said yes, thinking I'd lose it if I chose no, but that was the source file, so I assume that's why I got error, but initially thought info was in stat and mbtree files so would be ok. I tried to redo source as it had been reduced to zero, gave it same name as before, re-queued it, deleting first pass instructions, and moving 2nd part up to meet with original first pass, I then renamed vid output, and started it up again hoping to recover first pass, and move straight to encoding 2nd. This did not work, I got an immediate error, which follows in log.
MeGUI automatically assigns vid output same name as avs script, which is taken from source, so then do I always have to rename vid output file? This has been working, not sure what went wrong here. Less probs like this, or none when outputting vid to mp4, but I wasn't sure if that was going to give me longer remux times than working with just mkv.

Thanks a lot,
rlr

[runLoganrun]

follow up question: re: other error "can't write to stats file" do I have to specify that location everytime? It seemed like it was doing it automatically, but didn't in this other case, so when it went to perform 2nd pass, got error.
thx