Problem with Mixture Model and I/O

A VAX VMS user is having trouble with Mixture models. The problem has to do with I/O to logical unit 17 ("FILE17"), which is performed only for Mixture models. The error is FOR-F-INVLOGUNI, invalid logical unit number unit 16640 file The error occurs in routine DAT5, called by FNLMOD, called by NONMEM. I suggested that he change the OPEN statement in NONMEM's OFILES subroutine from OPEN (UN(17),FILE=FN17,FORM='UNFORMATTED') to OPEN (UN(17),FILE=FN17,FORM='UNFORMATTED',LRECL=1620) but this does not help. Has anyone tried Mixture models in VAX VMS? If so, did you run into any problems? Did you use population or individual data? This user has individual data: TOT. NO. OF OBS RECS: 562 TOT. NO. OF INDIVIDUALS: 562