I didn't ommit. In the script I listed above I included TRAJ command as:

! OPEN FILES, FILL SERIES VIA TRAJ
open read unit 1 file name popclipidsnowater.dcd

I have one file only, popclipidsnowater.dcd. What else should I include?

Also, in the output, I got no errors in opening the trajectory file:
CORREL> ! OPEN FILES, FILL SERIES VIA TRAJ
CORREL> open read unit 1 file name popclipidsnowater.dcd
OPNLGU> Unit already open. The old file will be closed first.
VCLOSE: Closing unit 1 with status "KEEP"
VOPEN> Attempting to open::popclipidsnowater.dcd::
OPNLGU> Unit 1 opened for READONLY access to popclipidsnowater.dcd

CORREL>


Thank you,