Replace colour brush stopped working

I was working today on a .cpt image, using the replace colour brush to swap between three colours.  I had almost finished when the programme hung and I got the error message box up "Programme not responding. Close programme now or wait for it to respond".  I waited, but it didn't respond so closed it.

Now when I open the .cpt image, replace colour is doing some strange things.  It will alter a colour which is not either the back ground or foreground colour selected with the picker tool.  It completely wipes out some colours and lines with the foreground tool, whilst it leaves others alone.

I have checked for updates.  The programme says none are available.  I am using Photo-Paint X7 Home & Student, Version 17.1.0.572 and it is licenced to me.  I have run the "Repair" facility.  My OS is Windows 7 Professional and is up-to-date.

I have reloaded the image I am trying to alter, but the same problem persists, so I suspect it is software and as everything was working before the "Programme not responding" message, i suspect the issue is related.

Before I do a clean install, is there anything anyone can suggest please?

Thanks for reading

NW