Using NOT operator and filtering data

In a table I have one column as Workstream and another column as Cost centre. If I want to run a query to return certain values of the Workstream and also to exclude one value of a Cost centre (within the values of the Workstream) I use the <> operator on the Cost centre. This is on the same line as the Workstream criteria so it acts as an AND condition. I have checked the outcome with and without using the <> Cost centre so the outcome is correct, but when I come to filter on the data of the Cost centre column, it gives an error message "Syntax error (missing operator) in query expression 'Cost centre'." I click ok but I'm not able to filter on the Cost centre column as no filter values come up. My result looks correct but why do I get this error message and cannot filter?