Have you tried taking the comparison out of the variable?
Example:
Code:
if %actor.skill(backstab)% > 60
I haven't tested this but I think the skill() function should be used as
%actor.skill(skillname)% and then it will return the amount of practice a player has in the skill passed along in parenthesis.
In your case I think the mud is looking for the "backstab > 60" skill, returning "unknown skill", and not working as expected.
For testing sake you can try:
Code:
%echo% Backstab: %actor.skill(backstab > 60)%
And see what it'll print out.
Hope it helps!