You can use the PHP snippet on any PHP file that you want debug. However, this will not help with Mod Security.
I just installed Mod Security on my test server and tried the UBB backup. It failed with the 403 error after the first refresh. I checked the logs and this issue is related to the dumpdir (Absolute PATH to Backup Storage Directory) field.
I found a workaround. Create a directory
backup in your UBB admin directory and then use just
backup as your new backup directory:
At least this solved the problem on my test server.