Fix was suggested by this url:
Using PowerShell to resolve Sysprep problems involving App-X packages - TechGenix
which basically says to rename the state repository database files and windows will recreate them properly...
Rather than set up a scheduled task as described there I rebooted my machine into a command prompt (not safe mode but a command prompt) and renamed the following files:-
C:\ProgramData\Microsoft\Windows\AppRepository\StateRepository-Deployment.srd
C:\ProgramData\Microsoft\Windows\AppRepository\StateRepository-Deployment.srd-shm
C:\ProgramData\Microsoft\Windows\AppRepository\StateRepository-Deployment.srd-wal
C:\ProgramData\Microsoft\Windows\AppRepository\StateRepository-Machine.srd
C:\ProgramData\Microsoft\Windows\AppRepository\StateRepository-Machine.srd-shm
C:\ProgramData\Microsoft\Windows\AppRepository\StateRepository-Machine.srd-wal
e.g. C:\ProgramData\Microsoft\Windows\AppRepository\StateRepository-Deployment.srd renamed to C:\ProgramData\Microsoft\Windows\AppRepository\StateRepository-Deployment-Corrupted.srd
then rebooted my machine into normal mode. Bingo - windows recreated the database files and started updating again...
so far so good...