We had the same issue with our mirror.  I used the following document from the Books which explained how to setup the certificates and it fixed our issue with connections.

ms-help://MS.SQLCC.v9/MS.SQLSVR.v9.en/udb9/html/5d48bb98-61f0-4b99-8f1a-b53f831d63d0.htm

Hope this...

In the Enterprise Manager in the linked server tab you can go to the properties of the linked server and on the security tab you can change how you want...