>>>

>>>ODBC Error: 0 Error: [Microsoft][ODBC SQL Server Driver]Communication link failure
>>>

>>>
>>>Does anyone know what the ODBC Error 0 means? Any other suggestions?
>>
>>I can only guess - the numbers come from the server, i.e. server telling you something went wrong - IOW you did talk to the server, and it didn't recognize you, because of bad handle or whatever. No connection, no number, so I guess this error comes from the driver itself, telling you it got nothing from the server.
>
>It makes sense; the server didn't recognize me (maybe because I wore a different jacket :)
>At least, now I know what causes the case(s) when a connection failure never recovers. As far as I know, this only happens with one customer. I will keep monitoring.
>Thank you.
>
>UPDATE. I re-read your message and noticed you mentioned the handle. I will log the handle number too. Just to see the value in the cases when ODBC error is 0. Thank you.

I added logging the conn handle to the error log. When the ODBC error is 0, the conn handle is a valid number.
Also, good thing: I added a code that forces to reconnect (method suggested by Walter Meester and Mr. Schneider) and the connection is restored. Even when ODBC error is 0.