Ok, you are right, the issue seems to be somehow layer related. the one line seems to be on layer2, while the rest of the component is on layer0. I had layer0 turned invisible so the line would not delete.

I usually must have the layer set visible as I have had the main model on the different layer for awhile.
Should I change the way I am using the layers? I did this mainly so I can make 2D exports as the drawing progressed without any of the work area visible.

Not sure if my model needs changing, but at least I know whats going on now!
Thanks so very much for your help.

the components themselves are fairly simple. once the line goes highlighted it stays persistently. When I click out of the component it will remain highlight blue within the component and its copies.

iMac running OS Lion sketchup make 2013 free version.
Tried to re-visit an old component piece and change the geometry but it wont let me delete the lines now.
I did a push/pull of a lower surface and tried to delete the line once they were co-planer. But now the line just stays highlighted blue once I hit delete key, or use the pulldown tab "erase"

New objects seem to still work. I was in the middle of working and all had been fine for some time.

Tried to delete a line from other existing components with the same results, no delete, just a darker blue line.
Nothing seems to be locked.
Thanks for any help!