it's not saying that you HAVE a virus. it's saying that the .exe file has been modified and this MIGHT be due to a virus. it also MIGHT be due to a crack but many companys are too PC to start accusing customers haha.
i'm not sure where to lead you, but i can tell you that what you're looking for is whatever is modifying the .exe file be it a crack (you'd know if you were using a cracked program) or a virus or whatever.
have your virus scans come up clean?
have you totally uninstalled nero and run the nero clean tool for good measure?
have you reinstalled from the ORIGINAL INSTALL CD?
if you've done all of these things and you're still having problems, i know i'm stumped...
regarding the "nero virus checker" that you keep referring to, i'm not even sure this exists. nero is not a virus scanning software...I'm pretty sure it's only recognizing that the .exe is modified, NOT looking for viruses...