This error is because the default setting for the Connection type is set to TCP/IP + HTTP, instead of just TCP/IP.

To change this setting, browse to your Applications folder, then to the Citrix ICA Client Folder.

- Launch the Citrix ICA Client Editor.
- On the Network Connections tab, click on the “Default Settings” button towards the bottom left. On the “Making a Connection” tab, you will see an area for Network Protocol.
- Click on the drop down box and change the setting from TCP/IP + HTTP to just TCP/IP.
- Save your settings and try connecting again.