temporarily rejected during MIME ACL checks: unknown ACL verb in "acl_rml_avas"

Hi,

I am running Exim version 4.34 with exiscan from the exim4-daemon-heavy 
package on debian backports

My config files contain :

acl_smtp_mime = acl_rml_avas

av_scanner = clamd:127.0.0.1 3310

and my acl contains :

acl_rms_avas:

deny message = This message contains malware 
  demime = *
  malware = */defer_ok

accept

However every message passed results in the error :

temporarily rejected during MIME ACL checks: unknown ACL verb in 
"acl_rml_avas"

Full exim4 debug shows no useful information, can anbody explain this 
error or suggest what the problem might be

Regards

Rob Fulton