Cannot remove manually configured L7 policy ASM

Normally this means that the policy in question is still associated with an object in the configuration. I would start by double checking this. If it is not in use by any object, and is not deleting, I would open a case with support.

You can reach support by calling 1-888-882-7525 or internationally 800 11 ASK 4 F5. Make sure you have your BigIP's serial number available as you will need it to open the case.