Fail to link 64-bit Code

I have a working 32-bit software library written in Fortran with low-level stuff in C/C++ It has worked for years.

It is fine.

When I re-build the library in 64-bit mode, none of the C functions are linked in. I've checked the linker options, and they all seem to be right. The project appears to be referencing the 64-bit libraries.

Would someone mind just looking some sample  INTERFACE code and tell me whether there is anything at all that would cause a problem 

      SUBROUTINE PBZQS(MODE, IXORIG, IYORIG, NX, NY)

      INTEGER MODE

      INTEGER IXORIG, IYORIG

      INTEGER NX, NY

      INTERFACE

        SUBROUTINE JB_ZBSpecInquireImageSize(MODE, IXORIG, IYORIG, NX,

     1      NY)

          INTEGER MODE

          INTEGER IXORIG, IYORIG

          INTEGER NX, NY

          !DEC$ ATTRIBUTES C, ALIAS: '_JB_ZBSpecInquireImageSize' ::

     1      JB_ZBSpecInquireImageSize

          !DEC$ ATTRIBUTES VALUE :: MODE

          !DEC$ ATTRIBUTES REFERENCE ::  IXORIG, IYORIG, NX, NY

        END

      END INTERFACE

      CALL JB_ZBSpecInquireImageSize(MODE, IXORIG, IYORIG, NX, NY)

      END

The linker comes up with:unresolved external symbol'_JB_ZBSpecInquireImageSize

Reassurance from someone "that should work" is all I need.

I observe that the project includes the library comdlg32.lib. Is that going to be right for a 64-bit application?

Is there an easy way to look at the contents of the .lib file that is being linked in?