Delphi: why breakpoints from time to time are not usable (green highlighted line on IDE)?

Question

From time to time I lose breakpoint functionality in Delphi.

I thought this to be a Delphi 2009 issue but now I have also it in Delphi XE.

In Delphi 2009 by

Answer 1

In my case, I was setting breakpoints in a unit that whilst open in the IDE was not part of the currently active project. Such breakpoints also show as green. IOW I was not on the right page at all.

(I discovered this after trying all of the above .)