dll problem in 64-bit machine

Hi,

One of our customer is using a windows 7, 64-bit machine. He is using our .net dll and registered it on the machine. But after copying the chunk and running Dynamics GP 10, he does some operation and gets the following error:

Unhandled object exception:
Class not registered
EXCEPTION_CLASS_OBJECT_EXCEPTION
ExceptionSubClass:-2147221164

While the dll seems to be working fine on other workstations.

Any ideas?