That code looks as though it may be from
one of my scripts written for GIMP version 2.2 (nearly six years ago); as such it has nothing to do with the GAP plug-in and it is too old to work with the version of GIMP you have installed. You need to search your scripts for one called "Letter Drop" or somesuch, and remove it.
If I recall correctly, I have never updated the script for GIMP 2.4 or GIMP 2.6, though perhaps someone else has. I did attempt earlier this year to create an updated version, but experienced some hardware failures* whilst in the middle of that task and have never gotten back on track (after months of cobbling things together with duct tape and baling wire, I have finally bought a new computer, which I just got operational yesterday).
Maybe after the holiday season, I will investigate creating a version for GIMP 2.8
* I'm not sure whether curiosity will actually kill the cat but leave your case cover off your computer for too long** and that feline curiosity will certainly effect the demise of temperature-sensitive, fan-cooled components on that computer's motherboard in short order.
** "Too long" in this instance was about 90 seconds.