If you have FileMaker Advanced:
1) Launch FileMaker Adavanced without trying to open this file.
2) Enable the script debugger
3) open the file and use the debugger to cancel the script when it pops up in the debugger.
This is one of the major headache removal benefits of using FileMaker Advanced.
If you do not have Advanced:
Do you have more scripts defined in that file besides this one problem script?
If so, Set up a different file with an external data source reference to the problem file. Perform a script in this second file that uses perform script to perform a script in the problem file--any script except one that closes the file.
Run that script in the second file and then use the Window Menu (or the Show sub menu in windows) to find and bring a window for that file to the front where you can open file options and remove this script from the OnFirstWindowOpen script trigger setting.