I have an RTD server implentation that is working fine with Excel 2003, but
not with 2007. #VALUE errors are shown when trying to use it with 2007.

I created a simple test project to try and narrow down the source of the
problem, but have not been able to uncover any useful information.

The closest I've come to finding a meaningful error message has been by
executing the following .vbs test script:

Set x = CreateObject("Rtd.Server")
x.ServerStart Nothing

The error message returned when running the script is:

test.vbs(2, 1) (null): Library not registered.

I have debug code in the constructor for the class that implements
IRtdServer and have confirmed that the class is being initialized
successfully. Any calls to the IRtdServer interface, however, fail with the
above error message.

Any idea what the problem could be?