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This article explains the steps that you may take to address the most common causes for the error 'An error occurred when creating instance for extension' which may occur in new extensions or in extensions that has recently been updated either in the control center or had their package updated and prevents them from working as intended.
When I attempt to run a new extension it fails to do so and generates the error message "An error occurred when creating instance for extension" in the logs.
The most common cause is that the extension is unable to access the code in the package meant to provide the extension with its functionality.
1. Restart your services. In the event that a extension is added or updated it will be unable to function or account for the update until a restart has been carried out.
2. Verify that the Assembly type follows the format "<namespace>.<class name>" in order to ensure that the extension is referencing the correct part of the package it is meant to use.
3. Verify that the class/constructor the extension is meant to reference is not set to private/protected or similarly inaccessible. In the event that it is private/protected, edit the access modifiers of the class to ensure that the class is accessible to the extension.
Please note that in the event that you need to correct your setup based on step 2 or 3 you will also need to restart services.