VMS Help UIL, Compile Time Errors, UID_OPEN  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  SEVERE:  The compiler could not create the UID  file  noted  in  the
  message.    A   UID   file   holds   the   compiled  user  interface
  specification.

  USER ACTION:  Check that you have write access to the directory  you
  specified  to  hold  the  UID  file.   If you have a large number of
  source and include files, check that you have not exceeded your open
  file quota.