Restrictions of the type:
variable must be >= %Player%.Held(False).Count give an 'expression does not resolve to a numeric value' error when the function does resolve to a numeric value and the restriction works.
Anything in the expression field that doesn't start with a number seems to give this error message when you press the OK button on the restriction editor.
%Variable1% gives the error, but
42+%VariableArray[%Variable1%+1]% does not.