sometimes when you install mirc in the same dirrectory as invision (like i do), if invision is installed first followed by mirc some of the .ini files in the main directory will be over written by the new mirc files. so all the startup info is lost, and the new clean mirc will load. i don't know if this your case but make sure you install mirc first then install invision. and you should be ok.
hope this helps.