You Have Used an Operator that is not Compatible with the Data Types Specified

From Xojo Documentation

Error message

You tried to perform an operation on data types that don't support the operation. For example, multiplying strings, dividing Booleans, etc.

Examples

Dim c As Integer
Dim d, e As String
Dim g, h As Boolean
d = "Ted"
e = "Alice"
c = d * e // error
c = g / h // error