It seems the diff() trigger function is broken. Just using the default templates I get "evaluation failed for function" for the following entries:

{mysql1:vfs.file.cksum[/etc/passwd].diff(0)}

>0

{mysql1:system.uname.diff(0)}

>0

{mysql1:agent.hostname.diff(0)}

>0

{mysql1:system.hostname.diff(0)}

>0

{mysql1:agent.version.diff(0)}

>0

All other items look fine.