I have noticed every now and then when using Remote Desktop Connection for Mac that I am unable to connect to Windows based computers. Initially I thought the issue was related to specific versions of Windows 7 and then when that turned out not to be the case I thought it had to do with the Remote Connection Settings on the Windows computer specifically the “More Secure” and “Less Secure” setting when configuring RDP on Windows. It turns out neither of those were the actual problem and it really is just the fact that the computer is connected to a Domain or Domain Controller.I was able to make connections using actual Domain accounts however not the local computer accounts which not only included users in the Remote Desktop Users group but also Administrators that by default should be able to make Remote Desktop Connections. Below I describe some of the basic items that should be confirmed to not be the case however I still suggest that you uninstall Remote Desktop Connection for Mac and install CoRD: Simple RDP Remote Desktop.
There are numerous reasons that you may either want to connect to Windows Remote Desktop on a different port or have Remote Desktop listen on a different port. The primary reason I wanted to configure this was my ISP does network scans every couple of months and if you have external ports listening they will suspend your service in an attempt to both cut down on viruses, spam, and to get you to upgrade your service to a business account that allows you to run servers. I wanted to be able to connect to a Windows Vista box at my house remotely and one of the ports included in my ISP’s scan list is the RDP (Remote Desktop Protocol) TCP port 3389. To get around this you can either configure RDP to run on a different port and simply use your router to directly NAT through the new port or I suggest you simply using Port Forward on your router to route another port from the external IP address to the TCP RDP port 3389 on the Windows computer running Remote Desktop. Below I describe connecting to a port other than the default TCP port 3389 from the Remote Desktop client.