One thing that often comes into play in situations like this is the fact that all OPC communication is handled by the FactorySQL service, which is a windows service running under the SYSTEM account by default.
Quick clients run under the logged in user, so they’ll appear different to the remote machine. You can try a few different things to verify this:
A) Change the account that FactorySQL runs under by going to Services (Control Panel->Administrative tools), right clicking FactorySQL Service, selecting “properties”, and then going to the “Log On” tab.
B) Search the forum for how to run FactorySQL as an application instead of a service.
If those work, you can either leave it like that, or open up the dcom settings on both machines to allow the service access. There are a few posts around here that talk about basic DCOM settings, and how to turn on DCOM logging in order to help track down the problem.