Here are the steps that seemed to fix the problem for me:
Deleting all profiles from device (iPad in my case)
Settings - General - Profile delete any relating to your app
Deleting all profiles from iTunes on iMac
Finder - Library (GO with ALT pressed displays this) - Mobile Device - Provisioning Profiles
delete all provisioning profiles you see here. This is where Xcode sees any when choosing your profile.
In Xcode - in both Projects and Targets
Set all code signing to None
Archive your project - in Xcode Product - Archive
You will be told no profiles exist - choose Fix Issue. Your provisioning profiles will be downloaded into the Library - Mobile Device - Provisioning Profiles (the folder we previously cleared.) In future these will be your options when setting your Project and Target code signing.
In Organiser
Export your archived product and choose the team Profile (or any that have been downloaded) as code signing.
Drop the ipa into iTunes and install.