Hi,
I think that error appears when the script processes the code in the file for more then 60 seconds, or, perhaps it runs into an infinite loop, or redirect again and again to same file.
Without seeing more of your code we’re not going to be able to give you a good idea of what’s causing this but, take a look at your loop and find out what is determining $book, make sure it’s not auto-incrementing with the rest of your loop since that error tends to indicate an infinite loop.