Ok i found out after much searching that I had the Buffer size on the Scarlett Mix Control set to 20ms I changed it to 3 ms and that was giving me dropouts so I increased it to 6ms and that seemed to work for a mid sized project with about 15 audio samples in 5.1 surround however it would not export and I had to do it in mono.
I originally thought I was having a driver incompatibility problem with Windows 7 and cubase 7.5 coupled to the 18i20
Also I read with interest that it is suggested that the driver be replaced with Asio4all??? where do I get this?