I tried changing it to the = it lets me be able to do the dates and the contract number with no problem but if I want just dates and location it says I need to put something in the contract number also.

WHERE SV00300.DATE1 Between (@Start_Date) and (@End_Date)and SV00300.LOCATNNM = (@LOCATNNM)

OR(SV00300.DATE1 Between (@Start_Date) and (@End_Date)and SV00300.Contract_Number = (@Contract_Number))