Intermittent failed test connections to SQL ODBC

Got a strange problem with an ODBC connection from an app server to a database on a SQL server. The app server is 2003 server. The DB server is 2008R2 with SQL 2008.
When I create the odbc connection and test it, it works the first time, but then the next connection attempts all fail with the error:
Attempting connection
[Microsoft][ODBC SQL Server Driver][DBNETLIB]SQL Server does not exist or access denied.
Disconnecting from server

A constant ping from the app server shows no dropped packets.
When I try the same odbc from a different app server and the same db server, it connects ok every time.
Any ideas on what might cause this?
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Jim P.Commented:
On the SQL server side do you have Named Pipes turned off?

NP depends on constant access to the original DC to keep the SID active. Change it to TCP/IP and see how it goes.
CashbuddiesAuthor Commented:
But it works fine form the other 2003 app server, wouldn't that setting affect it too?
Jim P.Commented:
The way Named Pipes works is that the app server first connects to the DC. Then the DC provides a token and redirects it to the SQL server. If the app or SQL server is losing connectivity to that particular DC the individual token is no longer valid.

With TCP/IP the app server goes directly to the SQL Server and says "Hi, I am appserver1. I want to get data. Here's my SID." The SQL server then says to any DC "Here's a SID. Is it valid?" The DC then says "Yes" or "No".  But if connectivity drops from appserver1 then SQL will go to any DC the next time with the question again.

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CashbuddiesAuthor Commented:
Thanks jimpen, named pipes fixed it
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Windows Server 2003

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