How to get the Value in code-behind?

I'm trying to get the Value property of the FCKeditor in my code-behind file. I've added the following in the file:

protected FredCK.FCKeditor txtText;

, but the compiler complains that it doesn't know what FredCK is.

I also have the following at the top of my aspx-file :

<%@ Register TagPrefix="FredCK" Namespace="FredCK" Assembly="FredCK.FCKeditor" %>

It still does not work. If I take away the:

protected FredCK.FCKeditor txtText;

the editor shows just fine.
What is wrong????

please help me,
/Andy