Data precision in textures (shadow mapping)

Hi!
I got some problems with setting up my shadow maps.

I've created a FrameBuffer Object with the following settings:

glGenTextures( 1, &mOGLDynamicTextureID );
 
glBindTexture( GL_TEXTURE_2D, mOGLDynamicTextureID );
 
glTexImage2D( GL_TEXTURE_2D, 0, GL_RGBA16, 
		          size, size, 
		          0, GL_RGBA, GL_FLOAT, 0 );
 
glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
 
glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );
 
// Create a frame-buffer object
glGenFramebuffersEXT( 1, &mOGLFrameBuffer );
 
glBindFramebufferEXT( GL_FRAMEBUFFER_EXT, mOGLDynamicTextureID );
 
glFramebufferTexture2DEXT( GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, mapID, 0 );