This happened to me recently. For an error message regarding sh3.exe there seems to be no option but an uninstall & reinstall.....follow the fine advice in other posts. However, I also found that I was getting messages about the upgrade not being possible because a help file (I forget which, i think the english help file) was an unrecognized version - if you get this message, delete the helpfile (or move it somewhere else) & try again, it should work.
You may get a Starforce error that tells you that you have a virus - you probably don't, there is a solution for this problem here:
http://www.subsim.com/radioroom/show...667#post407667