I'm using modern algebra's bitmap-addon. I removed the scripts that you think would cause a problem but nope.
Meaning you tried removing the Bitmap Addons script?
Line 133 is simply the line that calls the regular initialize method for a Bitmap, so I am guessing it would occur with or without the Bitmap Addons script. I'm assuming the error is that it failed to create a bitmap, which likely means that the graphic you are trying to open either does not exist or is not a valid file type. Alternatively, that you are trying to load a bitmap that is too small or too big.
Look into that. If you find no solution, then recreate the error in a new project and upload it.