Vista - Error message using remote desktop to connect to Server 2003

I am getting the following Logon Error message when connecting to Windows
Server 2003 from Windows Vista Business: "The terminal sever has exceeded the
maximun number of allowed connections". How can I correct this problem? Also
when I cliked Remote Desktop Help it tells me that Vista Business can not
connect to computers running Windows XP. Is this true? The remote computer is
running Windows XP but the server is Windows 2003. Please help!!!

I forgot to ask does the Administrator need to click allow all versions of
Windows to connect. Because when I talked to him earlier he kept telling me
that Windows Vista doesn't connect to earlier versions of Windows. My
computer runs Vista Business, the server runs Windows 2003, the host computer
has Windows XP. I hope this clarity helps.