Hello,
I'm still testin different configurations, different templates, but I get casual errors.
When I think I've found the right configuration and I do a stress test Im' proud that I've solved the issue. I do the last try and I get the error.
I also use minimal templates, to elimitate eventual scripts, but same result.
I kind of casual error.
Of course, if I eliminate the calender the orders are Ok, I get the variants included in the main Article.
I will try to update joomla to last version 3.2.2 and see if it could elimitate eventual conflicts.