Hi,
there are more problems, that can prevent your proggie from running on other systems.
The first one is, that NT like systems are more strict in controlling PE header info, so try to find some program that will check it for you (I'm quite sure I've seen it somewhere, if it is your problem and you won't be able to find it, maybee I could send it to you).
The second problem could be relocations. If you unpacked your proggie, then it probably misses reloc section, because packers do it themselves; but when unpacked program runs on other system, then could be loaded to other base adress then prefered one and then it'll surely crash. If this is the case, then you have several possibilities. You can try to rebuild relocations - probably lot of work, or you can make a loader or inject code to make needed modifications after proggie is unpacked in memory.
Hope it helps.

least