Need help with below issue.
I am picking up on a old project on CMS 11 for some fixes and when trying to load the CMS edit section, I get error as Bootstrapper.aspx not found. "System.ArgumentNullException: 'Value cannot be null.Parameter name: UserName'".
Your logged in session might be struggling to load assets in the modules folder.
Reinstallling the nuget packages worked for me. Thank you.