operation not supported irule error

Looks like you have a very long iRule in place (and possibly other rules assigned to the VS?). I'd suggest you check for any earlier (or later) redirect or respond commands that might match a particular connection more than once. Rather than use 'return' check the logic and flow of the rule to ensure there will only be one match (with no return commands used).

Happy to help if you are prepared to post the entire rule (suitably redacted).