Any time, I try to start a macro on a distance of around 1 ft, I see on my display at the place, where the residual number of fotos is shown, a mark saying and the cam does not trigger, only if beyond 1/2 meter
It means you need to be at least 1/2 meter from the subject.
What shooting mode are you using?
What lens are you using?
The Nikor Micro lenses have a special limit switch for closeup shooting.
Have you tried the manual focus mode?
Remember when you are macro focusing, the focus distance ring sets the magnification and the distance of the sensor plain to the subject sets the focus. So you may also need to move the camera to achieve a focused image. Some shooters use a focusing rail on their tripod.
Your lens may not focus that close, so the camera will not release the shutter. What lens are you using? "r15" is not an error. It always displays when you half press the shutter release. It's showing you the number of images remaining in the buffer.
If you're using your Sigma 18-200mm lens that you have listed in your profile, that lens' minimum focus distance is 45cm.
Welcome to Nikonians! (r15) is not an error. It sounds like you are trying to fucus on a subject that is closer than the minimum focus distance of your lens. Use Manual Focus mode and set the lens at the minimum focus distance. Then try focusing on your subject. Move back until your subject is in focus. Good Luck and Enjoy your Nikons!
You are right, I may have been to close to my target using my Sigma 18-200. Nevertheless this message r 15 appears again and again and the shutter does not release, even if I'm more than 45 cm away, but the tele is fully moved out on 200. Also in auto mode using the fully extended tele the AF does not work correctly, so that I have to activate the MF. May this be something faulty or still an "error of mine"?
(r15) is the number of shots remaining before the buffer is full, not an error code. In AF-S (Single Servo AF mode, the shutter will not release unless focus lock is achieved. If the focus confirmation indicator (green dot on the left side of the viewfinder display) shows arrows instead of a dot the AF system has not locked focus and the shutter release will be disabled. This is most likely the problem that you are having. It is more common at close distances or when the AF target has little contrast. Good Luck and Enjoy your Nikons!
The "r15" message (which as others have said is not an error code) always appears when you press the shutter release. In normal situations, it's only displayed for an instant so you won't notice it. But when the camera cannot focus - for whatever reason - the display catches your eye.
The camera may not be focusing because you are too close, because your subject has insufficient contrast (like a plain wall), or for one of several other reasons. I'll bet there is nothing wrong with the lens or camera.