VMS Help CC, Messages, NOADD  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 Message        <Context> "<expression1>" and "<expression2>" cannot
                be added.

 Description    Because of their types, the two expressions cannot be
                used as the operands of the addition operator.
                Either both operands must be arithmetic type, or one
                operand must be a pointer to an object type and the
                other must be an integral type.

 User Action    Modify the addition to use valid types.