Hi,
Yeah it could be a corrupt DLL or a faked DLL or an outdated DLL. Either way it seems to be finding the DLL file but not the routine in that DLL so a new DLL seems to be needed. Sometimes they are on the install disk so you might try installing the DLL by itself or else look in a Cab file for that DLL if possible. You might also have to install from a different operating system if the DLL is in use and you cant stop it from being used so you can install a new one, or maybe from 'safe' mode.
What we hope is that this is the DLL that is bad and it's not a whole chain of DLL's. Sometimes one is bad and once you fix that, you get another error in a different DLL, then another, etc., until all the DLL's are fixed. As Matt pointed out, it's usually simpler to reinstall the program from scratch that way any registry errors will get fixed too. A reinstall sometimes has it's drawbacks, but sometimes that's the only way.