I have seen this in a couple DNN 6.x installations. You know there is text in an html module, and then when you go to "Edit Content" the editor opens and the text appears to be gone.

If you happen to select-all [CTRL+A] and then manually change the font size, the text reappears and consequently gets re-sized by your actions. So now you understand that the text was in there but the default font size was 0.

This is because the RadEditor does not specify a default font-size in it's css file.

To fix this, you need to create a text file named editor.css and insert the css code to format the default font-size. Use this:

html {font-size:12pt;}

Save the file and place it in the portal default folder. Typically that is the portal 0 or 1 or so numbered folder.

After that, your text will be visible in the editor.