Invalid Class String


When the process is being run with administrative privileges the user is unable to get Elmaster Design started properly.


Error messages at start of Design that says Failed to load Master Concept dlls and invalid class string.


To make it possible/easier to switch between parallel installed versions resources are registered during the initialization of the application. The registration is done for the user who is logged in.

If the application is run by another account – even if that account has high privileges – the part of the registry being used is not the same as where the references to the resources have been set up.

It is a limitation that the acad.exe process about to load Elmaster Design must be run by the logged in user.


To confirm if processes you initiate are being run by your logged on username one can often determine by opening a command prompt and looking at its title bar if it says administrator or not.

Another way to determine if you have this problem is by looking at the acad.exe process via Task Manager. Go to the information pane and select the columns to show via the context menu on the column headers. Choose to show elevated privileges. If your acad.exe process is running with elevated privileges that means it is being run as the administrator account.


If you are using the context menu on the icon and Run as Administrator – don’t.

Instead run in normal mode by clicking on the icon in start menu och double click on the desktop icon to start Elmaster Design.

Usually, this problem occurs when the user temporarily gains elevated privileges to install new software. Via policy or similar management, the processes initiated by the user are impersonated and run by the administrator account for the duration of the installation period. If that is the case, let whoever gave you the elevated privileges know when you are done. When impersonation ceases, the problem ceases.

Preventive measures

Avoid running the acad.exe processes as administrator. Run it as your logged on user.

If users are temporarily given local administrative privileges for installing software, it is advisable to plan ahead and schedule the installation at a time when the user is not supposed to be productive using Elmaster Design.

Also available in format for download and attachment: Invalid Class String.docx

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