CodeWarrior and .def file

I'm developing a static interface DLL, which is not supposed to require a .def file.  When I build from the command line, I get a warning about a missing .def file, but it links OK.  But when I import the same mmp file to CodeWarrior, I receive the following link error:

The target type requires a .def file, but none was found in the target

My mmp file looks like this:

TARGET                  [MyDll].dll
TARGETTYPE           dll
UID                        0x1000008d [MyUid]
SYSTEMINCLUDE     \epoc32\include
USERINCLUDE         .
SOURCEPATH          .
SOURCE                 [various source files]
LIBRARY                 [various libs]
EXPORTUNFROZEN

Anyone know why I'm getting this error and how I can avoid it?

Mike