wcl2wbt.dll is a stub between WCL and WidComm stack.
There are 2 dlls. One is in <WCL_INSTALL_DIR>\redist folder and the other one is in <WCL_INSTALL_DIR>\redist\old folder. It is strongly recomended to use DLL from redist folder. This DLL is based on newwest WidComm SDK.
But if you are running 2 stacks: Microsoft and WidComm then the new wcl2wbt.dll can cause a problem. So in this case you should use wcl2wbt.dll from old folder.
Again: wcl2wbt.dll from <WCL_INSTALL_DIR>\redist is recomended.
wcl2wbt.dll from <WCL_INSTALL_DIR>\redist\old can be used only if you run Microsoft and WidComm stack on the same PC at the same time.
P.S. Windows Vista and Windows 7 does not have "clean" WidComm stack. WidComm runs on those platforms as an extension to Microsoft Bluetooth stack. So those DLLs are not requeired for those platforms. However, it is not bad idea to redistribute them.
