Error: The data types varchar and varchar are incompatible in the '&' operator

I am trying to concatenate two columns to bind to a listbox in c# to display like "id - name" 
SELECT ProductID, Name, CustItemNum, CustItemNum & ' - ' & Name AS itemNumName FROM Item AS it INNER JOIN JITVendors AS jit ON it.Catalog_Code = jit.Catalog_code WHERE jit.VendorName = 'SanMar' AND it.ProductID NOT IN (Select ic.productID From Item INNER JOIN ItemCollection AS ic ON ic.ProductID = Item.ProductID WHERE ItemProfileCatalogID = '3017') with the code listed above I get the following error:
Msg 402, Level 16, State 1, Line 1 The data types varchar and varchar are incompatible in the '&' operator.
Is there something I am doing wrong, or is what I am attempting not possible? Thank you
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