Error : Content controls have to be top-level controls in a content page or a nested master page that references a master page.

when I make a directory on my root, and in that directory I put a masterpage and a web form ... I get always an error : 
Content controls have to be top-level controls in a content page or a nested master page that references a master page. 
 
Does somebody know what the problem is ? Is it possible you can't set a masterpage in a directory ... ?
Kind Regards,

Joeri Pansaerts.

From Bruges, Belgium :)

i've founded ... I had to nest my masterpage ...
Kind Regards,

Joeri Pansaerts.

From Bruges, Belgium :)

Hi Joeri Pansaerts,
I am receiving the same error as the one posted here, Could you please share your solution with me.
I am using a single Master Page.
Thank You,
Sudhe

Hi Sudhe,
 Are you using 2 masterpages ?
Kind Regards,

Joeri Pansaerts.

From Bruges, Belgium :)

Hi Joeri, Thank you for the reply.
I am using a single master page, however I had figured out the solution.
Thanks once again,
Sudhe

hi,

I also geting the same error, I am using single master page and a web form.

please can any one help me to solve this problem.