IDD_DIALOG1 is the name of the dialog resource. You need to make sure you have
#include "resource.h"
listed where you include your dialog header file.
In your case, you might have named the files K11.h and K11.cpp, so in your K11.cpp, you should have something like this at the top of the file:
#include "resource.h"
#include "K11.h"
At times, you will get the error even if you have the includes correct. This happens because the IDE fails to notice that you have added a new resource. In that case a Rebuild All will normally solve the problem.
<Edit>
Note, that this only addresses the compilation error you are getting. Handling a button click is pretty simple, but there is nothing in the code you have posted related to that.
</Edit>
Soren Madsen