In some instances OPC Inbox will display an error message stating "No accessible overloaded ...", this can be resolved by following the steps provided below:
1) OPC Inbox requires SP1 for .NET v1.1. This can be downloaded from http://www.microsoft.com/en-us/download/details.aspx?id=33
2) OPC Inbox should be ran as an administrator for best usage.
If this solution does not work, or if you expirence dificulty please do not hesitate to create a Help Desk Ticket from https://controlstation.freshdesk.com/support/tickets/new