A few notes and suggestions--
- the file "nptprod.pdb" has an odd extension for a binary trajectory file; usually .trj or .dcd are used
- when not computing energy, use of the NOUPDATE keyword is highly recommended as part of the initial CORREL command
- specify the MAXTIME value explicitly, to e.g. 200
CORREL MAXT 200 NOUPDATE
You may still have trouble, esp. if NAMD is involved; in general, unless the initial PSF was created with CHARMM and exported as an XPLOR PSF for use with NAMD, you can expect problems.
There can also be binary file incompatibilities, if the trajectory was produced on a machine with a different architecture (big- vs. little-endian). CHARMM itself does not handle that very well at all.