CS0246: The type or namespace name 'bl1' could not be found (are you missing a using directive or an assembly reference?)

Hi friends,
                  I have a problem like this" CS0246: The type or namespace name 'bl1' could not be found (are you missing a using directive or an assembly reference?)" i created a namespace by name bl1 and in it i created the classes. the code is working perfectlly on my local system but when i tried to work it on server it is displaying this errors. how to resolve this issue if any one can show a solution it would be a greate help for me.
the code is something like this:
bl1.BL obj = new bl1.BL();
    protected void Page_Load(object sender, EventArgs e)
    {      }
and the code in .cs is as fallow
namespace bl1
{ Go to the complete details ...