

Note: If you are using a pre-3.0 version of Horizon Client for Mac, you cannot select the PCoIP display protocol. Workaround: Use Horizon Client for Mac 3.0 and select the PCoIP display protocol when you connect to the remote desktop.

in the Windows 7 virtual machine and perform the steps in VMware KB 2059786: Establishing a RDP connection with a Windows 8.1 desktop from Horizon View Client. Workaround: Install Microsoft update 3080079: Update to add RDS support for TLS 1.1 and TLS 1.2 in Windows 7 or Windows. This problem occurs because TLSv1.0 is disabled by default in Horizon 7 version 7.0 and later. After you install Horizon Agent 7.0 in a Windows 7 remote desktop, you can no longer use Microsoft Remote Desktop Connection Client for Mac 2.1.1 to connect to the remote desktop.If it's the second issue I would strongly advise against using the old Horizon Client due to security issues.
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VMware will likely completely remove RDP at some point so I think it would be best to switch to Blast or PCoIP. The list of file extensions associated with Microsoft Remote Desktop Connection Client for Mac - Program for remote control of Windows desktops from Apple. This is one of a few known issues in the Horizon Client for Mac 4.8 release notes.
