/sys$common/syshlp/helplib.hlb CC, Messages, LONGPREFIX  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 Message        Prefix string too long.  Truncated to "<newprefix>".

 Description    The specified prefix to the #pragma extern_prefix
                directive is too large for this platform.  The prefix
                will be truncated.

 User Action    Reduce the size of the specified extern prefix.