unresolved external symbol error (How to resolve?)

[WhatMeWorry via Digitalmars-d-learn]

Linking...
01_06_coord_systems.obj : error LNK2001: unresolved external 
symbol _D11common_game12__ModuleInfoZ
01_06_coord_systems.obj : error LNK2001: unresolved external 
symbol _D14post_processor12__ModuleInfoZ


I've gotten plenty of undefined external symbol errors in my time 
but how does one approach a "unresolved" error. Does this mean I 
have more than 1 occurrence of the symbol and the linker is 
confused?

And what do the _ModuleInfoZs mean?

I've got a package called common_game which has a module named 
post_processor.d

Any suggestions?  Thanks.