Problems with Exch5.5 srv account change

I changed the service account as per the white paper
published by Microsoft Product Support on ‘How to Change
Microsoft Exchange 5.5 Service Account’ published May 22,
2000.

I did manage to successfully change and start the server
with all the services restarting properly. But, the POP3
clients are not able to authenticate. The following error
message is found in the Application Event Log.

——————————————————–

EventID: 13003
Source: MSExchange Pop3
Type: Error
Category: Authentication

Logon attempt from to has failed:
HrLookupCredentials() call failed with error A required
privilege is not held by the client..

——————————————————–

I reverted back to the earlier service account and
everything works fine. My environment is: NT 4.0 SP6 & MS
Exch 5.5 SP3.

I did go through the documentation once again and checked
all the settings with the new service account, everything
is fine.

Any ideas why this is happening? Help highly appreciated.

Thanks in advance.

Regards,

Sharad