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Was that when using Customizer? My guess is that it's just a glitch with the web system, and will work if you try again, maybe after restarting the browser. If you continue to get this error, trying another browser might help, but I'm just guessing.
Valid values are integers from 1 to maybe 15-20 or so... there isn't a limitation in the script, but Customizer might use too much memory/CPU when making large versions and crash in the progress.
If you need to make a larger version, please download the OpenSCAD file and do the compilation on your own machine.