Had the auto-payout issues with my pools as well. I figured out that users were putting in improper wallet address. Some used URLs and others just had strange randomness entered. A quick sort and visual check on the sendAddress field of the database shows the offending address. Once I removed the address, problem solved. The payout.php ran just fine.
I've had quite a few users email me with auto payout issues, only to email a few minutes later and let me know they entered in an invalid FTC address. Once they entered a valid FTC address, payout issues were resolved. If you're having auto payout issues, please double check that you've entered a valid FTC address as your payout address.