I had some problems loading a type library (TLB file) when building a Visual C++ project, so I wanted to have a look at the TLB file using the OleViewer. So I started the OleViewer as Administrator from C:\Program Files\Microsoft SDKs\Windows\v7.1\Bin\x64. When opening the TLB file I got the following error message:

LoadTypeLib(my tlb file) failed.
STG_R_FILENOTFOUND ($80030002)

The issue here was that I started the 64bit version of the OleViewer. With the 32bit version (present directly in C:\Program Files\Microsoft SDKs\Windows\v7.1\Bin), this error was gone, so it could actually load the file but I got another error message:

IDataObject interface viewer only supports IID_IDataObject

Solving this was easy but kind of confusing. I went to the View menu, unchecked “Expert Mode” then opened the TLB file. And the error message was gone. After that I checked it again but could still open the TLB file. Eveb after closing the OleViewer and opening it again, I was able to load the TLB file.

I’m still not 100% sure what happened here… Another thing I did after removing the Expert Mode and before reopening my TLB file was to open a few object classes in the tree on the left. At least of them was the Microsoft Web Browser (under Controls). So if unchecking the Expert Mode alone doesn’t help, you could try this.

It looks like the error message I got above means that iviewers.dll in-process server was not properly registered. The OleViewer uses iviewers.dll to parse the type library. Somehow after the things I’ve done above, the registration was fine. Of course if it still doesn’t work for you, you can try registering it yourself using regsvr32 iviewers.dll.

Somewhere inbetween I’ve also try using but also had a problem with the same TLB file (also it worked for others). After the problem was solved with OleViewer, OleWoo was also able to open the TLB file. So I guess OleWoo parses the TLB the same way OleViewer does.

And actually after that Visual Studio 2012 wasn’t complaining anymore about the TLB file. Before that I got the following error message on the line where I import the TLB file:

error C1084: Cannot read type library file: ‘my tlb file’: Error loading type library/DLL.

So it looks like Visual Studio had the same issue with iviewers.dll as OleViewer and OleWoo but unfortunately only said it couldn’t load the type library instead of giving me a more precise error message…

Even if I don’t really get what happend here, I’m glad it’s solved 🙂