After hours of tinkering with it and trying to figure out what was going on, I managed to do it (he says with fingers still crossed).
I checked through the image sizes and made sure that the Gallery images and upload sizes were all within sensible size limitations to fit the page. I also checked the NEXT GEN Scroll Gallery image sizes measurements.
By adjusting the image sizes, (as it seemed they might be a little overlapping slightly with sidebar widgets) I thought it might be a little overlap causing a clash with sidebar items/code, it seemed to resolve it a bit more, but not quite - I had managed to get Chrome and IE working with it, but Firefox kept crashing out time after time with a script error for NEXTGEN SCROLL GALLERY or by "not responding"
I then got a friend to view the website and he said that AddThis looked to be causing a problem his end. I turned off scroll gallery and the page loaded fine with no errors, but obviously no gallery.
I decided to uninstall NEXTGEN Scroll Gallery and reinstalled it and it now works. Rather odd, but it musthave been something in the upgrade or in the settings. Either way, it works now - touch wood!!
Good luck! Hope this helps.