why can't debug using GNU gcc compiler?

[whatx]

I set a breakpoint,and strike 'F8' to start debug.
But it popup a error dialog  showing "This project/target has no debuging info.please change this in the project's build options and retry...".
Then I try to open the project's build options --> Compile flags --> selected "Produce debuging symbols [-g]". But no use.
why?
thanks!

[Jenna]

Look if stripping is also set for the build-target, that would strip all debugging infos from executable.