Hi Krishna.
Plesk 11. now installed. Sadly no change!
My server provider ran tests, over the week, and have satisfied themselves that it is a WordPress issue, related to all the individual WP installs!
Interestingly, twoo of my wp installs have remained unaffected throughout. They are on different domain names to each other, and are using much earlier WP versions to all the other problematic ones!
Any ideas would be appreciated?
Regards
john v