MessageBox problem

Hi there. I have a problem whith the api function MessageBox. I create a window for OpenGL rendering. The style of the window''s class is CS_HREDRAW|CS_VREDRAW | CS_OWNDC and the style passed to CreateWindow is WS_MINIMIZEBOX|WS_VISIBLE| WS_CLIPSIBLINGS|WS_CLIPCHILDREN|WS_MAXIMIZEBOX|WS_CAPTION| WS_BORDER|WS_SYSMENU|WS_THICKFRAME. After creating the window, i set it the foreground window and give it the focus. Everything is right but when I call the MessageBox, the main window lost the focus, but the dialog isn''t showed. ¿Any idea?