Hi Mickey!
Just to be clear, I am going to assume that by module you mean a function or procedure in a module, if not, then you need to call it by the procedure name not the module name. That said, I usually use the keyword Call before the procedure name, but that shouldn't be your problem. When you get your error click debug to see where the compile error is(if you have already done this let us know where the compile error is). If the error occurs on the line where you call the function then check the spelling of the function name and make sure the function is public(although these two things should give you a different error). Make sure that you are sending the function all of the parameters it needs(again a different error should occur). Make the sure the function doesn't have the same name as another object in your database as this could easily confuse Access. Finally, you can try going to the buttons property window and click on the Event tab. In the OnClick line type: =YourFunctionName(). For this to work, you must make it a public Function in a module.
If none of this works then repost with the code of the function and we can see if there is a problem there.
hth
Jeff Bridgham
bridgham@purdue.edu