404 on Field Save

[Tom.]

/processwire/setup/field/save

The url above when saving a field is giving me a 404. It started happening randomly - anyone have any ideas on what could be happening?

Thanks

Tom

[BitPoet]

Any chance this is apache with mod_security enabled?

[Tom.]

Hey BitPoet, 

Mod_Security is enabled, however this has only just started happening. I've been using it for over a month now and this has only just started. It might be worth mentioning that this doesn't happen on a ProcessWire website hosting on the same server. It seems to have been the update to 3.0.8 that caused it? 

Thanks,

Tom

[BitPoet]

I wouldn't rule out mod_security then, it's famous for returning that kind of random errors, as there are a lot of parameters that work together to trigger an exception. If possible, I'd look into mod_security's log file to either rule it out or confirm the exact trigger(s), and go from there.