Error: Cannot Run External Application "Librarian"

Several users have complained about a persistent error when launching the Librarian. The most common reason for this error is the inability of the App to write into the Windows user profile folder.

Reason for the Error:

Microsoft Ransomware Protection through the 'Protected Folders'  is enabled. This prevents the App from accessing the user profile to Cache Library Data.

Solution(s):

Two possible solutions exist:

1. Disable Controlled Folder Access Control or

2. Create Exceptions (can be tedious) to allow access to the following location:

C:\Users\%USERNAME%\AppData\Roaming\Librarian

Below are screenshots of the Windows Security User Interface leading to the Controlled Access folder:

Activating Autodesk App Store Licensing

This is post is intended for first-time users of the App Store. If one of the following situations apply to you, please read further:

1. You have never downloaded and installed any plugin (paid or otherwise) from the Autodesk App Store.
2. You have purchased an App in Bulk and your license was assigned by the software vendor.
3. You just created a new Autodesk Account in order to activate a license for an App (or download an App)

If you are trying to run a paid App and you are unable to authenticate the license, Autodesk recommends the following procedure to activate your account:

1. Download and install a free app such as the Family Size Reporter
2. Run the App at least once after logging into Revit with your Autodesk ID.
3. Now run the paid App that you are given an entitlement for and you should be able to authenticate your licence without a problem.