If you go to line 822 in the rule file, is that in the middle of some DRC rule check that uses NET AREA RATIO? Right after a NET AREA RATIO statement, it is allowed to have an "expression" that describes more details about exactly how to perform the check. That error message indicates there is some problem in the expression. Is the rule check something you are comfortable posting here in the public community? Someone might be able to spot a syntax error in there.