Plugin Causing WP White Screen of Death!

Grrrrr. This plug-in has kicked me out of my site twice.

Line 152 in the php file is apparently the culprit
$this->_maps_model = new AgmMapModel;

Here is what hostmonster chat told me:

(9:59:54am)Tanner L.:
The problem appears to be with your "appointments" plugin.
(10:00:46am)Karen:
Ah - thank you - that is the main one I need to use! Can you advise any more info about it so I can advise the supplier? Thanks.
(10:04:09am)Tanner L.:
[09-Nov-2013 22:45:16] PHP Fatal error: Class 'AgmMapModel' not found in /home1/profetb3/public_html/publicaffairsrecruitment/wordpress/wp-content/plugins/appointments/includes/addons/lib/app_locations.php on line 152
(10:05:22am)Karen:
Can you tell me in English what that means please? Is it a fatal plugin issue or does it indicate incompatibility with something? Thanks
(10:06:07am)Tanner L.:
it could not find "AgmMapModel" in the file "app_locations.php" on line 152
(10:06:25am)Tanner L.:
it means that is missing from your files, or something was not updated correctly.

What is happening please? Is it something I am doing or is it something that needs to be fixed at your end. I have re-entered the appointment data twice so far and getting sick of it.

Related Issue #1
I am also having related issues (there was a post 11 months ago about it - some guy had the same issue - when loaded to show 2 months, it was showing December, then My Appointments, THEN November and it skipped months)..I fixed it by changing "2" in the shortcode to "1" - and I am NOT a coder.

Related Issue #2
I have also put in the NON_AVAIL dates (Xmas) and none of them are showing correctly. What is the go with this? How do you fix it and make it show the correct dates to be greyed out. It has picked completely different dates to grey out.

Thanks.