That would be because the IF() statement is looking for a True/False answer on the condition. Excel will treat most any legitimate non-zero and non-False value as being True. But the MATCH() statement will either return something when true or the error when it doesn't exist and so you are giving the IF() statement and error for the condition. you can enclose the MATCH() with ISERROR() or use an IFERROR() statement around the whole thing to catch the error.
