Everything EPDM has to be on the same version and service pack. Vault databases also have to be updated.
I don't think that's the issue. We have three vaults and the other two are working fine. The two other vaults are connected to different archive servers at different locations and they don't have this problem.
Our consultant said the versions aren't an issue here. The replication logs are clean with no errors. We replicate once each hour.
It doesn't appear to be a VPN tunnel issue because the person on the network with the archive server can ping the vault server successfully. I'm thinking it has to be some kind of network error on the client side. But the fix is just having me log into the vault and out again - really doing nothing more than that. Then the client can connect successfully.