I ran into this while working on a customer’s new DNN site.  The install went well and I thought all was good.

Usually my first thing I do is delete the DotNetNuke stuff off the home page and then I go to the admin site settings and disable the inline editing.

When I chose to update settings on the admin settings page I got the following error.

DNN Cannot insert the value NULL into column 'DefaultLanguage'

The first thing I did was to check the admin settings page for a Language setting and sure enough under “Advanced Settings” and “Other Settings” there is a default language pull down menu.  I noticed that I couldn’t fill it in, because the pull down menu was blank.

So my next step was Google.  (Yah, I know I need to use Bing more often now)  I quickly found what I needed and this is what it boiled down to.

Within DNN

1. Go to the Admin/Languages page
2. Click on the Edit Languages link in the upper left corner of the module
3. Select a language from the Dropdown list.
4. Check the enabled checkbox
5. Click the update button.

I got this information from the bottom of a bug fix page. And I got the bug fix page from my trusted DNNCreative websites forums.

I always like it when it is a quick and easy fix.  Go DotNetNuke!