Folder plugin - add new folder received error

Hi all,

I am testing Folder plugin and  activated OKAY.  Everything is working except when I tried to add a new folder and received error message below:

Internal Server Error

The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator, and inform them of the time the error occurred, and anything you might have done that may have caused the error.

More information about this error may be available in the server error log.

Additionally, a 500 Internal Server Error error was encountered while trying to use an ErrorDocument to handle the request.