Coverage Analysis does not provide coverage data for a DLL called by a .NET process. More than likely, the DLL in question is registered to the GAC (Global Assembly Cache). When a DLL is placed into the GAC, the symbols for that DLL cannot be loaded, preventing DevPartner from locating the symbol file [ pdb ].
The Assembly Registration tool by Microsoft reads the metadata of an assembly and will provide any necessary entries to the registry. In turn, this will allow COM clients to create any of the necessary .NET Framework classes in a transparent manner (Microsoft, 2013).
As it relates to the issue of no coverage data, remove the DLL from the GAC and reregister the DLL using the regasm command (Assembly Registration Tool). After registering with regasm, rerun Coverage Analysis and coverage data should be made available after the coverage session has ended.
Note: If the above information has not resolved your issue. Open a ticket with Support for further assistance and additional trouble shooting.
Microsoft (2013). Assembly Registration Tool (Regasm.exe). Retrieved June 4, 2013, from http://msdn.microsoft.com/en-us/library/tzat5yw6(v=vs.80).aspx