An expression of type %1 is not union-compatible with type %2

Error constant SQLE_SLERR_NOT_UNION_COMPAT
ODBC 2 state ERROR
ODBC 3 state ERROR
Parameter 1 The type of expression 1.
Parameter 2 The type of expression 2.
Severity 16
SQLCODE -1479
SQLSTATE 2FW72
Sybase error code 13093
 Probable cause