Unknown server tag 'FCKeditorV2:FCKeditor-Collection of common programming errors

So i`m getting an unknown server tag for FCKeditor in my aspx page. Here is the link to the source code

Among the solutions tried:

1)

2) Checked if the dll (FredCK.FCKeditorV2.dll) was in the directory.

Firebug gives me an: 500 Internal Server Error

AND

The actual error is: Parser Error Message: Unknown server tag ‘FCKeditorV2:FCKeditor’.

I have a similar page with the same code and for some reason it works and this one doesn`t.