I’ve seen some abnormal behaviour while installing Update Rollup 2 for Exchange Server 2010 SP3.
“The feature you are trying to use is on a network that is unavailable”
The installation refers Exchange Server 2010 SP3 source file (exchangeserver.msi) which I used to upgrade from Exchange Server 2010 SP2 to SP3. This should not be the case but I don’t know why it is referring to SP3 source files.
Either copy Exchange Server 2010 SP3 source file to the asking location or just browse it to the location where it is stored.