SAP Message Q8850 - Operator & is not permitted for one of the specified values

Diagnosis
The specified relational operator is invalid for at least one of the
specified values.

System Response
The following operators only work with numeric values:

'>, >='
'<, <=, ><'
The following operators work with numeric values and character strings:
'==, <>'
Procedure
Correct your entry considering the restrictions explained above.