It is probably broken or you haven’t installed it in lua/bin/ (not lua/includes/modules/) where DLL modules belong.
I would recommend not to use a outdated gm_bass module, if you don’t need too, as it could cause conflicts with the game’s Bass Lua bindings and so other addons.
For what do you need it, exactly?
Edit: If you need one for shared/server usage you can use gm_bass3. However make sure you know what you are doing.
Did you install the .dll files to ‘…/garrysmod/lua/bin’ and NOT ‘…/garrysmod/bin’?
Make sure that require() is filled with the right name too. Enter “bass” for gmcl_bass_win32.dll or “bass3” for gmcl_bass3_win32.dll and gmsv_bass3_win32.dll into it.