Sounds like you’re running into typical DCOM configuration issues.
If the computers are in a workgroup, make sure that the same local userid and password are defined on the workstations. Whether the workstations are in a workgroup or a domain, make sure the OPC server and the OPC client are running with/using the same credentials.
For troubleshooting purposes, try using a generic OPC client (e.g., KEPServer’s Quick Client) to get data from the remote OPC server.
Often times you can browse to a OPC server but you can’t get OPC item data because the OPC Enum service, which is responsible for telling other applications what OPC servers are installed on the computer, typically has no requirement for authentication and therefore will work. However, to connect and query OPC items, you do need to have the proper/matching credentials.