The latest Reader is 11.0.01, not 11.0.1. It is named Adobe Reader XI.
I did uninstall the Reader X and installed this latest one.
But it did not solve the problem, still could not open the problem pdf's .
I did find the problem was caused by the MS Office Click to Run error referred to in my original message. As far as I know we have no use for that on my wife's computer. Not sure how it got there. I uninstalled it and so far the problem pdf's open fine now. Problem solved.
Thanks for your help.
Frank M.