APM W3C Local Logging iRule

It looks like the ACCESS events and the HTTP events do not play nice together.

What version are you running, and what is your access policy doing? I've tested this on an 11.4 and 11.5 system without any errors.

I would also like to know where I can find a list of ACCESS:session data get variables?

There really is no definitive list, given that each process (ex. LDAP query, Kerberos SSO, etc.) will insert its own session variables. Your best bet is to either run an APM report in the GUI or dump the "created" session variables using the sessiondump -allkeys command in the shell. Here is a small list of common session variables though:

http://support.f5.com/kb/en-us/products/big-ip_apm/manuals/product/apm-config-11-4-0/apm_config_sessionvars.html?sr=35265198

Also would it be easier to log this data by using ASM?

You could, but you could also do the same thing using the LTM request logging profile:

http://support.f5.com/kb/en-us/products/big-ip-aam/manuals/product/aam-implementations-11-4-0/20.html?sr=33764514