I'm hoping someone would have pointers on this.

We have recently migrated our SharePoint 2003 Database on SQL 2000
to an instance running SQL Server 2005. All visible WSS/SPP
settings were transitioned to the new DB server and the web services
restarted per instructions found here:
www.microsoft.com/.../movewsdb
.mspx

When I attempted to shutdown the old database server, certain (I
believe only non-admin users) were unable to save document content
and some unable to access even the default of the virtual server.

Looking into this I noticed that under Database Server settings, the
old database server is still listed. When I attempt to remove it I
recieved a message indicating that existing sites used the database,
however the virtual servers content database was changed, so not
sure what's going on.

Configure Server Topology >> Database Server Settings:
Configuration database server: NEWSERVER\DBINSTANCE
Content database server: *NEWSERVER\DBINSTANCE, OLDSERVER
Component settings database server: *NEWSERVER\DBINSTANCE, OLDSERVER

The users that were unable to access the site received this type of
error:
Server Error in '/' Application
Cannot open log for source {0}. You may not have write access.

The user that was unable to save content recieved:
Retrieving overall status encountered error. Error code = 17

Hope this made sense. Let me know if you have any suggestions, etc.
on what might be going on.