The Calendar module doesn't recognize fields
I installed Calendar 7.x-2.x-dev, Date 7.x-2.x-dev, and Views 7.x-3.x-dev; then I created a "Test" content type to which I added a date field ("Start date").

When I edited the Calendar view, and added a new argument for the view (view arguments are called "contextual filters," in Views 7.x-3.x-dev), I followed the following steps:


I filtered out the list of arguments to show only the ones defined from the Date module; between the two argument types, I selected "Date: Date (node)."
On the settings page that Views shows after I selected the argument type, I selected the date field I added to my content type.










If you select "Date: Date (users)," then you will see all the date fields that are associated with users, as in the following screenshot.



Still, the field I added to my content type is visible in the list of fields shown in the settings page for the view argument.

The issue you are seeing is probably caused by compatibily problems between Date, and Views. I would try using Views 7.x-3.x-dev.