Ad 1. Yes, QuickOPC runs as 64-bit component under .NET 3.5 / Visual Studio 2010. You need to use version 5.23 (not the latest 5.30, which is for .NET Framework 4.5+).

Ad 2. Interoperability accessing 32-bit OPC server from 64-bit apps: It generally works, but there may be some minor issues. We have tried to overcome them to the maximum extent possible. Do not be too afraid: There are no issues in the OPC communication between the client and the server itself. The only issue we have seen can sometimes happen with server enumeration, i.e. listing all servers that are installed on the computer, and has to do with the OpcEnum service (and its versions) which may not “see” all the servers, depending on where in the registry it looks. Installing latest 64-bit OpcEnum helps, plus we have made some extra measures/workarounds as well. And, many applications connect to OPC servers that are hard-coded (by their CLSID or ProgID), and this issue does not apply to them at all. Once the server is identified, we have not seen any interoperability problems.

From: OPC Labs Contact Form - A.
Sent: Tuesday, April 22, 2014 2:22 PM
To: Zbynek Zahradnik
Subject: OPC Labs Contact Form - Switching to QuickOPC

[...]
Hello,

We have a 64-bit WinForms .NET 3.5 application running on Windows 7 64-bit to access 32-bit OPC servers (conforming to OPC specification 2.0).

I have the following questions:
- does QuickOPC run as a 64-bit component under .NET 3.5 / Visual Studio 2010?
- is there any interoperability issue regarding COM, when accessing 32-bit OPC servers from a 64-bit application through your QuickOPC component?

Thank you for helping us to decide if we could use your QuickOPC component.

Best Regards,
A