Lookup Function - Pay Rate Table


I'm trying to create a formula to pull rates setup on the Pay Rates table in PR. The Fields I used are "Employee" and "Job". When i use the lookup function on a custom public formula to look up a rate from my table i get an error "Too many Parameters". My formula is LOOKUP(Rate (PR Pay Rate Table),"RateTableName",Employee (PR Time),Job (PR Time)). If i modify the Pay Rate table to only one field such as Employee, i can get the formula to work. Why would the Lookup be limited if i add "Job" to the table?