Availability calendar view: lots of "Undefined variable", "Undefined index" and "Invalid argument" messages

Issue Summary

I just installed the agreservations module and enabled some modules of it, as i want to find out what each of the modules does and when I would need it.

Enabled modules:
Core:
- agreservations
- agres_conflict
Custom:
- none
Extra:
- agres_availability
- agres_views
Online bookings
- agres_categories

Ubercart not (yet) installed, as I am looking for a solution where online payment is not (yet) needed.

The PHP error messages I get on the "Availability Calendar" view:

In month view:
none

Switching to week:
Notice: Undefined variable: agrescurrentpath in include() (line 35 of agres_availability\theme\agres-availability-week.tpl.php).
Notice: Undefined variable: currentselectedweek in include() (line 35 of agres_availability\theme\agres-availability-week.tpl.php).
Notice: Undefined variable: categories in include() (line 37 of agres_availability\theme\agres-availability-week.tpl.php).
Warning: Invalid argument supplied for foreach() in include() (line 37 of agres_availability\theme\agres-availability-week.tpl.php).
Notice: Undefined variable: agrescurrentpath in include() (line 47 of agres_availability\theme\agres-availability-week.tpl.php).
Notice: Undefined variable: currentselectedweek in include() (line 47 of agres_availability\theme\agres-availability-week.tpl.php).
Notice: Undefined variable: currentcategory in include() (line 47 of agres_availability\theme\agres-availability-week.tpl.php).
Notice: Undefined variable: unittypes in include() (line 49 of agres_availability\theme\agres-availability-week.tpl.php).
Warning: Invalid argument supplied for foreach() in include() (line 49 of agres_availability\theme\agres-availability-week.tpl.php).
Notice: Undefined variable: by_hour_count in include() (line 58 of agres_availability\theme\agres-availability-week.tpl.php).
Notice: Undefined variable: day_names in include() (line 59 of agres_availability\theme\agres-availability-week.tpl.php).
Warning: Invalid argument supplied for foreach() in include() (line 59 of agres_availability\theme\agres-availability-week.tpl.php).
Notice: Undefined variable: cell in include() (line 65 of agres_availability\theme\agres-availability-week.tpl.php).
Notice: Undefined variable: units in include() (line 69 of agres_availability\theme\agres-availability-week.tpl.php).
Warning: Invalid argument supplied for foreach() in include() (line 69 of agres_availability\theme\agres-availability-week.tpl.php).

Switching to day:
Notice: Undefined index: span in include() (line 90 of agres_availability\theme\agres-availability-day.tpl.php).
Notice: Undefined index: values in include() (line 113 of agres_availability\theme\agres-availability-day.tpl.php).
(repeated about 130 times)

Switching to year:
Notice: Undefined property: stdClass::$field_agres_rdate in template_preprocess_agres_availability_mini() (line 516 of agres_availability\theme\theme.inc).
Warning: Invalid argument supplied for foreach() in template_preprocess_agres_availability_mini() (line 516 of agres_availability\theme\theme.inc).
Notice: Undefined property: stdClass::$field_agres_ref_unit in template_preprocess_agres_availability_mini() (line 530 of agres_availability\theme\theme.inc).
Warning: Invalid argument supplied for foreach() in template_preprocess_agres_availability_mini() (line 530 of agres_availability\theme\theme.inc).
(repeated 8 times)