[plt-scheme] mzscheme -t with binary files?

We're trying to create some scripts to deal with student programs. When 
we use mzscheme -t myteachpack.ss, and myteachpack.ss is a text file, it 
seems to work, but when we try it with something containing images 
(specifically Kathi Fisler's fabric-teachpack.scm), it doesn't seem to 
be able to recognize it as a module. We get:

default-load-handler: expected a `module' declaration for
`fabric-teachpack', found: something else in:
#<path:/u/cs135/marking/1/testSuite/fabric-teachpack.scm

The file in question loads into DrScheme just fine, both as a teachpack 
and using Open. Any ideas? Thanks. --PR