This happens a lot with SafeDisk protected games (although I don't know if that is what is used to protect Tachyon). It is quite likely that the copy wasn't 100% exact and that's why it's throwing the error.
You'll probably be able to get a patched .exe from GameCopyWorld or at least a No-CD patch.
Failing that, use the CDFreaks copy protection detector (or another) and check the copy protection for the game. Then, if it's SafeDisk or similar, use one of the generic process patchers available (again from GameCopyWorld).
I hope this helps.