Solution.
For some reason the admin rights on my PC have changed. Although my user account has admin rights, when I run PD12 as administrator everything seems to work OK. There is a difference between having admin rights and being an administrator (See Win 7 sites)
This problem has also affected other programs on my PC. Why the programs ran OK for a year until now then decided they need to run as administrator, I do not know.
You can set programs to run as administrator see http://technet.microsoft.com/en-us/magazine/ff431742.aspx
Hope this hint helps someone
Rgds
Win7 Home Win 7 Home SP 1, PD 13
Processor i5-4460 CPU @ 3.20GHz, 3201 Mhz, 4 Core(s), (RAM) 8.00 GB, Sys Drive 120 gig SSD, Data Drive 1 Terrabyte, Nvidia GeForce GTX 750Ii , Portable USB3 2 Terrabyte