As with most of the other responses in regards to back-button disabling, the better solution is to create a unique ID that is in a hidden field on the submission page; in the large processing script, the uniqueID should be checked to see if it has been processed; if so, don't do anything, if not, process the job and mark the uniqueID as done. There's numerous ways to create the uniqueID as previously described.

The key thing is that while there is JS code that can disable a back button, there are always ways around it (such as through menu options, key shortcuts, off-beat browsers that don't support such mis-features, etc). It's better to fix the problem on the server side than on the browser side where you have less control.

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Dr. Michael K. Neylon - mneylon-pm@masemware.com || "You've left the lens cap of your mind on again, Pinky" - The Brain