'The specified path, file name, or both are too long. The fully qualified file name must be less than 260 characters and the directory name must be less than 248 characters'.
Navigate to 'C:\Users\[User]\AppData\Roaming\Tools 4 Revit\Wall+ [RevitVersion] User Settings' - and open the PathConfiguration.xml that you will find in the folder. In the XML file, please edit the file path that is too long, shorten the path, or specify a different one. You will then be able to open the Configuration Files Location window as before.