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

 Message        <Context> "<expression>" is not an lvalue, but occurs
                in a context that requires one.

 Description    An expression that must be an lvalue was not an
                lvalue.  For example, the operand of the address-of
                operator must be an lvalue.

 User Action    Modify the expression so that it is an lvalue.