not sure if this will help or not, but have you checked the file attributes of the widget.php file? With my install (only 5 days old) I hecked the file attribute of said file and it was set to 644 (which means only Owner has write abilities). I know I have often had to on previous sites given some files a value of 777 or 776. (I use filezilla, not sure if these values mean anything to anyone else). Could this be to problem of the “You don’t have permission to access” error?
I know I have a default install as well. Was going to install this plugin, but due to all the problems I thought I would wait.