this is all too common. When the enum starts out its just a replacement for the lack of a boolean data type in C, and its used as a return code; true for success and false for error, but then what always seems to happen is that more error codes are needed; file not found, and so on. THe only real mistake is calling the enum Boolean rather than ErrorCode.
To avoid this, always call your true-for-ok/false-for-error enums something like ErrorType and use NO_ERROR or similar. Problem solved.
It's worse than that. It's the equivilent of YES, NO, TRUE, FALSE. So now you have to test for multiple values (did it return YES or TRUE?). And given that you most likely wrote or are using documentation that existed before GRAPHICS_DISABLE and GRAPHICS_ENABLE were added, you won't check for those. Not only that, but who checks for "other" in what is supposed to be a boolean test?
To avoid this, always call your true-for-ok/false-for-error enums something like ErrorType and use NO_ERROR or similar. Problem solved.