"The authentication service is unknown" on some Win98 machines when using DCOM

I am having headache with two Win98 machines. I am working in a domain. I have a ActiveX EXE program installed on a server (Win2k), and a client ActiveX EXE installed on client PCs. The client EXE will send a query to the server EXE, and the EXE will extract the data from Access database and send it back to the client. Some Win98 machines are working fine. I was not sure what modification had been made previously to make the client EXE working. For two of them, I receive the following message:

-2147023149 (800706d3)
The authentication service is unknown.

Using DCOMCNFG, I already set "Authentication Level" of the server's EXE to "None" and the problem still exist. One of the machines even have been reformatted and the problem remains.

I tried to install DCOMCNFG on the Win98 machine but it seems that I have nothing to modify.. most of them are greyed out.

Do I need to modify the registry? If yes, how?

Any help will be grateful. Thanks and hope to hear from you ASAP.