ASM my.logout.php3 Error 22

Hey guys, I'm relatively new to F5, ADC is my history. I've come to setup two separate F5 instances in different DC's and it's gone well on the one, the second DC I have pretty much the same setup as the first minus DNS servers, NTP etc. When using the APM module I need to front Citrix with APM, for this one DC I keep getting a redirect and reset to /my.logout.php3?errorcode=22.

I've done a "tail -f /var/log/apm" but this brings me no information to debug, I've tried searching via this site, google etc for that error code and nothing helpful has been found so far.

I've gone through the access policy comparing the working solution, I've imported it from the other box (modifying as required). As far as I can see its exactly the same minus the different AAA object.

Where do I go to find out what error code 22 is? Is there a better log to look at? On the working instance I can see loads of detail after I login, it's very useful, but seeing as I'm unable to get to the basic APM login form, I'm a bit stuck.

I can log with F5 but thought I'd ask here first.

Cheers.