When a SOLIDWORKS PDM add-in fails to load with the message:

Failed to load add-in
Reason: Class not registered

the cause often isn’t the add-in code or COM registration itself: It’s the elevation context in which the host application runs. Windows isolates COM registrations between two different scopes:

When you register your SOLIDWORKS PDM add-in (e.g. CardSync.dll) using regasm or the PDM Administration tool, it is normally stored under the current user’s profile (HKCU). However, if the host process like File Explorer, PDM Explorer, or even your test harness (Orca.Tests.exe – At Blue Byte Systems, we have developed our very own unit testing framework for add-ins), runs as Administrator, Windows will block access to any COM object registered per user.

That’s exactly what the “Class not registered” dialog means.

SOLIDWORKS PDM Explorer itself is not designed to run elevated. When your own executable or service is launched as Administrator, it now operates in a different COM security boundary and cannot see the user-level registration of your add-in.

In the example of the screenshot above, I’m debugging inside Visual Studio (ADMIN) and launching my process from there. The moment Visual Studio is elevated, every child process (including your test harness) inherits that elevation, and therefore loses access to the per-user COM registry hive.

Microsoft’s Official Explanation

Applications that are run-elevated (whether manifested as RequireAdministrator or selected via Run as Administrator), as well as applications run from an Administrator account where UAC is disabled, cannot access any COM objects configured per-user.

(Source: MSDN – “Manifestation” and Stack Overflow discussion)

How to Fix or Avoid It

• Do not run Visual Studio or your test tool “as Administrator”.
  • Keep it at normal user level so it shares the same registry hive as SOLIDWORKS PDM Explorer.
• Verify which hive your CLSID resides in:
  • HKEY_CURRENT_USER\Software\Classes\CLSID\{Your-GUID} → per-user only.
  • HKEY_LOCAL_MACHINE\Software\Classes\CLSID\{Your-GUID} → visible to elevated processes.
• If elevation is required (for example, when writing to Program Files), register your add-in for all users using:

Our Practical Advice:

If your application interacts with SOLIDWORKS PDM’s COM APIs, never run it as Administrator unless the add-in is registered per-machine.