You have connected ("opened") unit/handle 33 to the file boxdipol.dat, but there are no commnands in your input file that actually write anything to this unit.
How about using the ECHO command (for which the outputfile was defined with the ECHU command) instead of the WRITE? It would also help if you actually write something to the file ... eg:
ECHO hi this is a dipole moment: ?XDIP ?YDIP ?ZDIP
(see subst.doc for CHARMM internal variables)
or use the CORREL module