I'm getting the following strange error when deploying a Permission Set from a CS3 (Winter 13) Sandbox into NA13 (Summer '12) production org. Normally, there shouldn't be issues deploying between the two, but I'm fairly sure this error is due to the version difference:

Unknown user permission: AllowContacts20

A clip of the permission set source code with the above setting is below.

    <userPermissions>
        <enabled>false</enabled>
        <name>AllowContacts20</name>
    </userPermissions>

Has anyone run into a similar issue deploying permission sets between orgs of different api versions?

Best Regards,

Mike