No interface found but works fine everywhere else?

No interface found but works fine everywhere else?

I have an ASP.NET website I migrated/converted from classic asp to v4.0
There is a 3rd party DLL which is used and I need to register it using
regsvr32.
Now all of this works just fine on my local dev environment but also on a
test webserver. My environment runs WS2008R2 Enterprise + all updates and
iIS 7.5 The test environment using WS2008R2 Std + all updates and IIS 7.5
I have created several virtual machines with a plain environment to test
deployment and that works fine.
The live one however causes a problem. That is running WS2008 Std +
updates and IIS 7.0.
When getting to the page in question, I get a runtime error and NO idea
where to go about this:
Unable to cast COM object of type 'TAMOnlineUtils.clsMainClass' to
interface type 'TAMOnlineUtils._clsMain'. This operation failed because
the QueryInterface call on the COM component for the interface with IID
'{B0B5FC90-90A9-4DD9-A4C6-D779C905B322}' failed due to the following
error: No such interface supported (Exception from HRESULT: 0x80004002
(E_NOINTERFACE)).
at System.StubHelpers.StubHelpers.GetCOMIPFromRCW(Object objSrc, IntPtr
pCPCMD, Boolean& pfNeedsRelease)
at TAMOnlineUtils.clsMainClass.GetCertFileList(Object& sPath)
at TAMOnlineWebsite.Report.CalDisplay.DoDisplayCertAndData()
Any ideas anyone? Completely stumped.