Sorry, but I'm not sure what you mean. Html module content is inserted by DNN v5 and seemed satisfactory. After updating to DNN V6 occurred above error. There are four sites on the same DNN and update was conducted on a Norwegian-language sites. Could it be that English and Norwegian date setting is not the same code?

-------- DNN 5.6.03 works like this:
1) If you set the start and / or an end date for a module, so it works perfectly OK.
2) If you later want to reset the current date with an empty field, 'NULL', then the DNN system automatically set the value in the field to 12/31/9999.
-------- In DNN 06.00.00, this gives the following problem:
3) The update to the DNN to the v6, this is not valid for 'SelectedDate'. 'SelectedDate' Hubble pray Between 'MinDate' and 'MAXDATA'. Parameter name: SelectedDate that Telerik.Web.UI.RadDatePicker.set_SelectedDate (Zero Able `1 value) that DotNetNuke.Modules.Admin.Modules.ModuleSettingsPage.BindData () that DotNetNuke.Modules.Admin.Modules.ModuleSettingsPage.OnLoad (EventArgs e) .
4) Result: DNN v6 does not provide access to the module for any editing whatsoever of any kind.

Would that be the skin or container that is being used. As I am not having a problem with the text/html modules. Mine is working tine. I have a youtube video posted in the html of the module on my home page. It seems to be fine. Might be your container.

Try using the default container that comes with the upgrade and see if that helps.