Portable apps must be restarted

Portable apps seems to work fine on 50% of the computers that I use it on and most recently was working fine on computer at work (win NT 2000 i belive) yesterday and today I get the error unalbe to start must program must restart. I am able to run all apps on thumb drive just not protalbe apps menu. Still works fine on home PC and wife's PC both XP pro. Any suggestions?