OBIEE Inconsistent Datatype Error

Using Bins in Oracle OBIEE I was getting ORA-00932: inconsistent datatypes: expected CHAR got NUMBER error.

The error occurred when the datatype of the column was Number, but I had a mix of String and Number in the Bin Name.

Eg.

CASE WHEN <TABLE.COLUMN> IS BETWEEN 30 and 39 THEN '30-39'
WHEN <TABLE.COLUMN> IS BETWEEN 40 and 49 THEN '40-49'
.....
ELSE
<TABLE.COLUMN>
END.

Becomes

CASE WHEN <TABLE.COLUMN> IS BETWEEN 30 and 39 THEN '30-39'
WHEN <TABLE.COLUMN> IS BETWEEN 40 and 49 THEN '40-49'
.....
ELSE
'Other'
END