[HELP] Visual Basic dll protection

I experimented more. I renamed another DLL file to be the same as the one I modified. Looking to see if there was a checksum. There appears to NOT be checksum on the dll file.

I renamed an unrelated dll file to the one in question, and ran the program. It did not report any errors. I am interpreting this to mean that there isn't a checksum check at the time the dll is loaded... that infact there is something wrong with the dll file after I changed 2 bytes with winhex.

Any suggestions?

*EDIT* Checked the dll file with PEiD and it says overlay - "MS Visual C++ Method2 Overlay".

Using PE Explorer I can see the error code and something else about CRC check. Did they utilize a program to give it some kind of protection?