If it is a UNIQUE KEY, you will need to remove it using the ALTER TABLE statement.
alter table tbl_Payroll_SubType drop constraint IX_tbl_Payroll_SubType
But you may want to keep a way of getting that constraint back, as I am sure it was put in for a reason. If there are any foreign keys hanging off of this UNIQUE KEY constraint, those relationships will also need to be dropped.
Thanks so much! That did it. I was searching around for the constraint name, thinking that it would be called something different from the index.
The index and constraint were put in because the people who created the database didn't know what they were doing. There is already a primary key defined for the table and this index contains the primary key along with another column (which is also defined in another index).