Can someone please help me on how to remove white dot on this image. When i render it with diffuse enable on the glossy material on the floor and the cupboard at the right, the dot disappear but I was not satisfied with the render. However when I disable the diffuse on all glossy material the render was ok but I cannot remove the white dot. Even if I increase the sample of the 4 sphere light to 30 and the world background sample the white dot remain here. 
Do you have lights very close to meshes?
Yes, the two spot light that project the ies light is near to the projector support. And two sphere light at the back of the camera is near to its support socket but not intersect into the mesh. Should i put it far from its plug socket? Its not realist!
It could be a sampling issue, see here:
http://www.yafaray.org/community/forum/viewtopic.php?f=13&t=2654#p14573
Alvaro.
Those white dots are called fireflies. How long has this been rendering? There have been cases where fireflies appear when rendering for way too long.