It's possible that your webserver has been set to disregard execs.

Also, you can't pass parameters using the exec command, you have to use the include virtual syntax instead if you need to pass a query string.

Apache webserver docs:

The include virtual element should be used in preference to exec cgi. In particular, if you need to pass additional arguments to a CGI program, using the query string, this cannot be done with exec cgi, but can be done with include virtual, as shown here: