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

 Message        The controlling expression "<expression>" has <type>
                type, which is not scalar.

 Description    An execution control expression does not have scalar
                type.  This is not valid.  An example of an execution
                control expression is the expression following the
                while keyword in a while statement.

 User Action    Change the control expression to have scalar type.