You've fixed my problem. I had two versions of a project seven extension active, so I de-activated the old one and my problems disappeared. But also - at the same time- the share extension asked for my serial number, so maybe deleting the .dat file finally kicked in? I also tried using the share "current page" feature on page with a php extension, and it worked.
Do you know if there are any disadvantages of renaming pages from .html to .php? Obviously, I'd have to re-direct and change links, but is there any other disadvantage? We are re-designing our site to make it more mobile-friendly, and I don't know if changing the extension has any impact on appearance.