1) I wouldn't put this in a formula, I would put it in the Report/Selection Formulas/Record, so that only the records that meet the criteria are allowed on the report (unless that is not the intent).
2) the error message typically means that the data types don't match...something like: a number = a string or a boolean = a date, it doesn't make sense.
If this is used solely in a formula, it will return just true or false, and if that is the intent, then all is well and good, if not, more will need to be added to the formula.