Since this is Solaris and not Windows it probably isn't the same issue but I've seen those exact error numbers for Windows boxes when the client is an older (but supported) version than the destination Media Server and the backup was configured to use client-side-dedup over the LAN (not WAN so link speed wasn't an issue). I really saw this when I jumped my Media Server Appliances from 2.6.0.2 to 2.6.1.1 and the clients were still running 7.5.0.7.
Disabling client-side-dedup always seemed to "fix" the errors but isn't a good option...
As soon as I upgraded the client (I was lucky, none of the boxes were User Controlled boxes so the approval process was short) to the same version as the Media Server, backups with client-side-dedup enabled started working right again..
It seems that the "backwards compatibility list" only applies when using basic backups, not any special features like client-side-dedup.