This error always indicates that your script has grown too large. Whenever this error is reported, consider AppleScript broken and you should quit Script Debugger and relaunch as soon as you’ve saved your work.
Your script will work in Script Editor for a while because Script Debugger imposes greater demands on AppleScript. However, your script is nearing the limit for Script Editor as well and its only a matter of time before you start seeing the Internal Table Overflow error there too.