Sharepoint Server 2007 generates event log entry every 5 minutes – “The SSP Timer Job Distribution List Import Job was not run.”

I get the following error logged into the Event Log every 5 minutes:

The SSP Timer Job Distribution List Import Job was not run.
Reason: Logon failure: the user has not been granted the requested logon type at this computer

In addition, OWSTimer.exe periodically gets into a state where its consuming almost all the CPU and only killing the process or restarting the Sharepoint services fixes it (although I'm not sure if this is a related or seperate issue).

I have tried the following (based on various suggestions floating around the web), all to no avail:

• iisreset (no affect)
• Added the Sharepoint and Sharepoint Search service accounts to Log on as a batch job and Log on as a service policies in the Group Policies for the domain. I went into the Local Computer Policy on the Sharepoint server and verified that those policies had actually been applied
• Verified that the Sharepoint and Sharepoint Search service accounts are both in the WSS_WPG group
• Verified in dcomcnfg that the WSS_WPG group (and indeed the Sharepoint and Sharepoint search service accounts) has local activation rights for SPSearch.

Any more suggestions would be valued.

Thanks