Assuming that you device is not offline and the server can communicate with it correctly, then this may be a DCOM configuration problem. Browsing is initiated from the OPC client, whereas subscriptions require callbacks that go in an opposite direction. It is a common mistake to forget about configuring DCOM for an access that goes FROM the OPC Server BACK TO the OPC client.

If your OPC client supports it, try to invoke a synchronous Read, because it has similar execution characteristics as a Browse. If the sync read works, but async Read and subscription update do not, the DCOM is the most likely reason.

See also this question about configuring DCOM for OPC.