The Type Library Importer (TLBIMP) converts the type definitions found within a COM type library into equivalent definitions in a common language runtime assembly. The output of TLBIMP.exe is a binary file (an assembly) that contains runtime metadata for the types defined within the original type library. You can examine this file with tools such as ILDASM.exe.
The Type Library Exporter (TLBEXP) generates a type library that describes the types defined in a common language runtime assembly. The entire assembly is converted at once. You cannot use TLBEXP exe to generate type information for a subset of the types defined in an assembly.
You cannot use TLBEXP.exe to produce a type library from an assembly that was imported using the Type Library Importer (TLBIMP.exe). Instead, you should refer to the original type library that was imported with TLBIMP.exe. You can export a type library from an assembly that references assemblies that were imported using TLBIMP.exe.