You are right - first step is determining if it is a browser side error, or server side. Do you have a modem with lights? When you click and get the error, is there internet traffic?
If there is no error in your error logs, then it sounds like it must be browsers. It could still be server side with the script itself generating the error and not any server error (so no error would be in the logs).
Does the script you are using on the server have any "Debug" modes in it you could turn on?
When it does this on you, have you backed up from the error page and looked at the source code to make sure the script hasn't generated bad html/js, thus causing the browser to error?
Does it error EVERY time on that page, or do you have to reload the page to get the error to go away?
Have you tried turning on scripting errors in your browser to make sure there isn't some weird js error that could be causing it?