Linux says a kernel module has an unknown symbol, but another loaded module provides it
I had similar issues compiling Advantech drivers. The operative phrase here is really "no symbol version".
Section 7 of http://lxr.linux.no/#linux+v2.6.33/Documentation/kbuild/modules.txt provides details on module versioning. Section 7.3 is of particular interest. The simplest solution for me was just to stick in a KBUILD_EXTRA_SYMBOLS line (as described starting at line 526 of modules.txt above). In your case, you could probably just add a line like
KBUILD_EXTRA_SYMBOLS := <driver_root>/kernel/core/Module.symvers
to the top of <driver_root>/kernel/USB-4761/Makefile.