the use of commenting features is database dependent (which you didn't list). my guess, is that you are using access - which doesn't provide this functionality.

but i've also experienced similar problems with mysql, if so, then you might try adding a crlf between the command and the comment (for some reason this has always worked with our injection attempts).

i don't see a problem with using the provided syntax with ms-sql (except that it doesn't support the # comment), or with oracle.