Everytime I try to join a server, i get this message(s) :
Your map [maps/ns_(insert map name).bsp] differs from the server's.
or:
Your dll.[cl_dlls/client.dll] differs from the servers.

I recently installed V3 Beta 4 and it worked fine, but since yesterday I was unable to join any servers, but i could still create LAN games. Pls Help. Thks In Advance.

Uninstall NS... install using ns_install_v3_b1.exe
after that simply patch it up with the latest beta 4

it'll work

or you could just delete the map, set cl_allowdownload 1 and connect to a server running the map.