Hi I am having problems opening the files to gain access to the full length backing tracks. I can download the shortened versions included with the lessons but I am unable to open the guitarpro.gp5 files. Can you tell me what software I need to gain access to these files please.

To open a Guitar Pro file you need this software (there is a free trial) : http://www.guitar-pro.com/en/index.php
There is also a free alternative software that opens the Guitar Pro files here : http://www.tuxguitar.com.ar/download.html