Connection Error of RealVNC in Windows 7

Hi,
A free version of RealVNC is used to connect remotely to the computers on our domain. I was trying to connect RealVNC in one of the computer with OS Win7 but I was unable to connect for my work. There were no problems of installation and again no connection problem from Win7 to the other computers on the domain. But I got a problem when I tried to connect from any other computer to the Win7 machine. Always a black screen appeared and nothing to do. Any kind of help will be appreciated.
