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

If the file you're trying to set breakpoints in is part of a DLL, you need to make that DLL active by double-clicking on it in Project Manager so it turns bold, and then build it. Then the blue circles will show up next to lines where you're allowed to set breakpoints.