Perhaps the user the Web server runs as doesn't have permission to open that file, or isn't logged in. If the open fails, the error will be in $!; printing that will probably help you figure out what's going on.
Comment on Re: Windows Share Access from CGI Script
I'm getting "permission denied" in $! Presumably this works from the command line because I'm logged in and have permission. How do I give access to my CGI script then? I've granted everyone full access to the share in it's settings.