>>>I'm not sure which type it is. Anyway, I dropped them in App_Code, I'm having this problem now
>>
>>Did you happen to add a reference to the existing project already? If so, remove it. It's either an eternal/referenced DLL or it's part of the same project. You don't want to do both.
>
>I didn't add a reference except for the fact I added these classes on the Toolbox.

Did you drop this control on a form after adding it to the toolbox? If so, the reference was automatically added.