Basically you will be redirected to the project startup page if the configuration files are missing - as in your case, it seems that the whole application data folder is missing. What I would suggest is to restore a previous copy of your project ( a backup one ) or extract only the App_Data folder from a backup of the project, and then replace the license file, which is located in App_Data/Sitefinity. Unfortunately there is no built - in mechanism in Sitefinity for restoring deleted folders on your machine, but if you do not have any backup files, you can ask an administrator to perform a system restore or other kind of backup of your machine.
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