Hi Everyone, I have spent the last day trying to work this out for my partner and I have a certified fix, which is GUARANTEED to work! I think the problem can come when the old phone you have is not upgraded to the latest software. I am not 100% this is the cause however the only reason I can come up with, so....Presuming you still have your old phone, upgrade it to the latest software and do a back up, if you dont try this anyway as it should work.
Please find below a step by step guide on how to DFU restore your handset, you can either choose to restore from a back up or just restore, I chose from back up and this worked.
Switch on PC and load iTunes
Do not plug your phone in just yet
Make sure handset is switched off - just hold the on/off button until it goes dark, not a complete reset.
Plug one end of the cable into the PC (not in to the handset just yet)
Press and hold the home button on the handset while it is switched off
Whilst holding the button (do not let go until you see the itunes plug in it will appear eventually) Plug the cable into the handset and keep the home button pressed until you see a pop up appear in iTunes
Let go off the home button on the handset
On iTunes, select the update and restore option
Agree to terms and conditions
If all is well, iTunes will start downloading the iOS.
Once downloaded, at the top of the iTunes window, it will show you it is installing the software.
Once complete, test Handset
After a very unhappy partner this worked and everything updated as it should do.
Hope it helps.