Let me explain..
When I open up MechVM usually it is to unpack or view the contents of a PRJ file, but I usually click "View MW2 File" before I click Unpack archive.
If I click "View MW2 File" first then I click unpack archive it refuses to unpack if i decide to select the same PRJ file.
It is no problem for me to reopen the program and click unpack archive, but it is rather annoying. I do not mean this to be a major complaint, just thought it should be known that there is a pitfall so to speak.
I would suggest if possible on the condition that this happens the program should close the archive and free the file lock or something to that effect so that does not happen.
(Discard this if a hastle, it really is not a big deal)

