Fatal Error Appointments+

I can no longer activate my appointments+ plugin. When I do I recieve the following message –

Cannot redeclare class URI_Template_Parser in /home/allgooda/public_html/wp-content/plugins/appointments/includes/gcal/external/URITemplateParser.php on line 30

I had an update message for the plugin. I updated the plug in and then bang!! I can no longer access the plugin. The only thing that shows up on my site is the short codes. The plug in will not activate.