Is the web server running on Windows or Unix/Linux? I'm not too familiar with Windows permissions, but if it's on Unix or Linux, check that the user the web server runs as (might be 'nobody', 'apache', etc.) has write permission to your file. ls -l myfile.pl will tell you what the permissions are currently set to.

As for the path, what I meant was this: You said that on the server, it refuses to write to the file. You didn't actually say it was reading successfully. Is it?