RE-add witness fails

I start with 3 servers, in High Safety mode with witness. I disconnect the network cable for the witness. Then I remove the witness from the mirroring session:

ALTER DATABASE db1 SET WITNESS OFF

I reconnect the witness network cable. Now I cannot add the witness back to the mirroring session (either with TSQL or thru the GUI). Here is the error message:

Msg 1433, Level 16, State 4, Server SERVERA, Line 1
All three server instances did not remain interconnected for the duration of the ALTER DATABASE SET WITNESS command. There may be no witness associated with the database. Verify the status and when necessary repeat the command.

I have to stop mirroring (SET PARTNER OFF) and then reconfigure a new mirroring session to be able to include the witness.

If I don't disconnect the network cable, I am able to remove and re-add the witness to the session, no problem.

Is this behavior expected?

Thanks in advance.

Regards,

Michael Lawson

I found my problem: my witness was at RTM. After upgrading to SP1 I was able to re-add the witness in the scenario I gave.