I know these forums are for TIE Fighter but maybe some of you have played X-Wing as well. Is there any reason why I cannot advance from mission to mission I have invulnerability in X-Wing?

thats normal, in x-wing you're not allowed to advance in a campaign when cheating.

in tie fighter you advance when cheating, but your score gets reduced by about 90 percent.

you can use a pilot that has all campaigns completed and play the missions in historical combat, though

such a pilot should be included in xwing for dos (topace5.plt), you can use this tool http://xvtedicion.es/ingles/descargas/programas/c_programa_ing.php?id=13 to convert it for use with xwing for windows

edit: narg, i mixed that up, that pilot is included in the 1995 version of xwing, sorry

I personally see it as bad design if you can't progress if you cheated, i mean sure you should be penalized, but not stopped from progressing.

Presumably, that's why it was changed in the later games.

Maybe so but then try playing it with the cheats off, invulnerability and unlimited weapons were more made available so players could make a recon of the mission first and decide the best course of action, the game was meant to be played with no cheats (as any game should be) and is sometimes hard but possible.

This is also why GOG needs to get the DOS Collectors CD-ROM as it modified certain missions so they became a bit easier to complete.

I am more about the story behind the battles, since each one has their own little back story and plot, seeing the outcome of those is far more important to me then the challenge of the game itself.