Hmm, I don't get any issues here, apart from GimConv stuffing up with the game_plugin (should dump if you don't convert GIM images).
I suspect that may be something to do with your system language there.  Rcomage doesn't support Unicode names as of now - I might think about trying to implement that.  Does your path to the RCO contain any Unicode characters?  If so, see if you get the same issue if you put the RCO in some place where the path does not contain Unicode.
Also, if you know how to use the command line, would you be able to test with that?

Thanks a lot!