I add this tag:
<%@ Register Assembly="FredCK.FCKeditorV2" Namespace="FredCK.FCKeditorV2" TagPrefix="FCKeditorV2" %>

and drag and drop the control from toolbox to the form Yet I got this:

Server Error in '/SolPortal' Application.
--------------------------------------------------------------------------------

HTTP Error 404 - Not Found.

what could be the problem?

Hi be sure to place the .dll file in the bin-folder of your application

Hi,

I already added the dll file to bin yet I got the error in runtime and I visited its site and counl't find any document or similar problem.

any idea what's going on?

Have you used this control?

I solved my problem and since I found many has the same problem, I write the solution hope it could be useful for others:

1-      Download the latest version of FCKeditor.Net  from:
http://sourceforge.net/project/showfiles.php?group_id=75348&package_id=137125

2-      Download the latest version of fckEditor from:
http://sourceforge.net/project/downloading.php?group_id=75348&filename=FCKeditor_2.6.2.zip

3-      Copy the uncompressed package of FCKeditor in the root of your project in ‘fckeditor’ folder.

4-      Add FredCK.FCKeditorV2.dll  as reference to your web.

5-      Add this line for registering assembely :
<%@ Register Assembly="FredCK.FCKeditorV2" Namespace="FredCK.FCKeditorV2" TagPrefix="FCKeditorV2" %>

6-      Add control tag to your page:

7-      Add this line to your web.config:

Or

Set the BasePath of the control on your page:

Quick question. When you say to "copy the uncompressed package of FKeditor", surely you don't literally mean everything in that folder because that includes samples and all kinds of stuff for other environments such as ColdFusion and PHP. Could you clarify exactly what has to be copied into the FCKeditor folder?

Thanks,
Kevin