I dont understand your question, you already posted the answer. When you start INLINE you are still in namespace __GLBASIC__, if you want to leave it, you do so with simply writing }, if you are done with your stuff, you need to reopen the namespace before you call ENDINLINE. So it looks this way:
INLINE
} // closed namespace __GLBASIC__, you probably are in global namespace now
// do that stuff here, that you dont want to be inside GLBasic namespace
namespace __GLBASIC__ { // reopen GLBasic namespace
ENDINLINE
BTW you rarely need to do this, most INLINE stuff that you probably do, can savely be done inside GLBasic namespace. I usually just opend my own namespace inside __GBASIC__, which also works fine.