The comments popup is working again!
If you have suddenly have problems with your comments system since new and improved Blogger, it could be because Blogger have changed the length of the BlogItemNumber to 18 numbers, too many numbers for a LongInteger field to hold. It is not possible to have integers of a magnitude larger than about 2.1 billion. So there you have it. You will need to change the field type to text and amend your script to fix the problem.