Thanks Brink & Bare Foot Kid, for getting back to me with advice.
Unfortunately, the default file types doesn't seem to be the problem, as all my files do have default programs associated with them. I can even select one of the alternatives from the right-click pop-up option menu. I can also open and use the Default Program application via Control Panel.
The error message comes up as soon as I click on "choose default program...", from the bottom of the pop-up menu. It's as though that dialog isn't associated with the "Open with'' application anymore.
When I can
get to the "Open with" application through other means, ..... the darn "Always use...." is greyed out, so it becomes a permanent selection / rather than temporary. Double checked the procedure on my other PC, and everything works as I thought it should.
I know I can sort a work-around out to re-select a default program, in a round-about way, ... but I'd just love to sort whatever has gone wrong with the right click context menu.
Obsessive compulsive??, ... haha .... probably, but I can't help it.
...... getting tired now .... feeling the problem may be in the "context menu handler", ....( but to be honnest, ... I haven't got a clue )... having searched around a bit more.
Just tried reading some of this: http://msdn.microsoft.com/en-us/library/ff521657%28v=VS.85%29.aspx
If anyone can translate something from the above, hehe .... or offer me another few crumbs of hope for what direction I might go, in searching out where a potential registry error has occured, I'd be eternally grateful
Going to sleep on it a bit,
G'night for now, and thanks again.