"Catastrophic Failure"

Hello,

I have written a simple OCX in VC++ 4.2 and have tested it successfully in
VC++, Visual Basic and Delphi 2.0.  However, when I try to invoke a method
from this control (for example, the About Box) in a Delphi 3.0 project,
I get:

Project raised exception class EOleSysError with message 'Catastrophic
failure.'

With the de{*word*81} stopped on ControlInterface.AboutBox in the associated
Lib_TLP file.  This happens no matter which method I try to invoke.  I
cannot even find a reference to "ControlInterface" in any of the help.
Can anybody see what's wrong here?  I am new to OCXs ...

Thanks,
Mark