This could be happening in the event that you had recorded a file upload. The scripting method for handling the multipart/form-data posts was done as a hotfix and hasn't been sufficiently tested. If you script a file upload and the file is a few MB, it is Base64 encoded and added to the script. This is not an ideal solution, as it should really add the file as a resource in the project and read it with a resource reader to prevent this. But development time allowed didn't permit us to implement this way.
What you can probably do is locate this line, hit RETURN on it, and append the next line:
abcdef016782476BD" & _