Grovel, scrap .... moans and sighs and begging for forgiveness.
It turns out that the Intelliguard feature of Spyware Doctor is blocking the launch of Calibre.
Again, sorry for the waste of your time but we did learn something.
After your last post, I realized that it must be something at my end and so I disabled Spyware Doctor (Something I don't like to do as I always practice "safe computing") Calibre launched just fine. Then I was able to narrow it to this one feature.