UPDATE: It looks like we have finally been able to sort out my issues,
the culprit - a USB hard drive connected via a USB hub 
I have no idea why this was causing a problem for the Virus, according to the computer the port the TI is on is separate to the port the hub is on.
Jorg from support (who is very helpful) says that USB drives can quickly eat up any available USB bandwidth, but in my non computer trained brain seeing as the ports are separate from each other I wouldn't have thought that would cause me a problem.
Anyway, the TI has been running flawlessly for the last couple of days so it must have been & if I have to disconnect the USB drive which is only used for Time Machine when working with the Virus - I can live with that.