There appears to be a maximum size that an AJAX response can be.
It you try to display more than about 250 timeslots on the booking screen, it will fail.
This only affects you if you plan to run
a lot of timeslots.
My test was 50/day (every 15 min from 7:00 AM to 19:30 PM)
I can display 5 days only.
If you need this timeslot density you will have to set the GAD grid to show less days. The default is 7. If I set my test site to display 5 days it works fine.
This is still under investigation. Maybe there is a server parameter tat can be tweaked.
# Additional #
Looks like it might be in the web server.
Apache has this..
LimitXMLRequestBody - "Limit (in bytes) on maximum size of an XML-based request body"
I cannot find how to change it. It may be set differently on your host and therefore vary the limit higher or lower.
#UPDATE#
This was submitted by a user..
In your forum you say that you don't know how to change this Apache parameter. It is explained here:
httpd.apache.org/docs/2.2/en/mod/core.html#limitxmlrequestbody
By putting
LimitXMLRequestBody 0
in the .htaccess file of your document root, this request limit should be disabled. If your host does not allow overrides this way, you can ask your provider to include the directive manually in the Virtual host configuration of your site. That could be the moment you discover that the hosting provider is not offering you the service you need.