This is an intermittent problem on 6 servers on 6 databases.
It occurred with 3 oracle 10g databases, and now that we've migrated to 11g, it is still occurring.
As soon as I hit any of the 3 websites, it intermittently issues this error when trying to retrieve data from the database:
ORA-12571: TNS:packet writer failure
If I refresh the screen, it retrieves the data fine, and it doesn't always occur, but it is a problem and occurs several times a week for many users.
The first 3 databases were not on a load balanced server but the 11g are used on load balanced websites.