Excel2003 could not load managed COM Component

[Jack]

Hi,
We built a COM object(let say, rtblink.dll) and extend RTD function by
implementing IRtdServer in our coding. The platform was .Net 1.1 , and
IDE is Visual Studio7.0. We use regasm to pu the COM object into
registry and use excel 2002 to launch that DLL, everything was fine.
Now we upgrade the developement enrionment to .Net2.0 , Visual Studio
2005(8.0), and Excel 2003. After we rebuild the project, the new
rtblink.dll could not be loaded by Excel 2003. To figure out the
problem, we make another COMCaller to load the COM object, it is fine.
And we try to use basis RTD functions in Excel 2003. It is fine,too.
And we use Excel to launch a unmanaged C++ COM Object, it is also fine.
But there are just something wrong when Excel2003 try to load this
managed C# COM component.
Could anyone give me some hint or tell me how to solve this problem?
Thanks.
Jack