Question : When I can #import a dll and when must I #import a tlb?

I see both semantics all over.
Yet when I try to import a specific DLL, which is of course a COM DLL,
I get:

fatal error C1083: Cannot open type library file: 'CarServerTypeInfo.dll': Error loading type library/DLL.
Error executing cl.exe.

Can anyone tell me what went missing in preparing this DLL?
How can I make it #importable?

Answer : When I can #import a dll and when must I #import a tlb?

Type libraries can be standalone TLB files or they can be embedded as a resource into a DLL (or an EXE). Therefore, whether or not you can use a DLL in a #import depends on whether it his an embedded type library.

You can use the OLE/COM Object Viewer to determine whether a DLL contains type library information:
http://msdn.microsoft.com/en-us/library/d0kh9f4c.aspx