that I can see the picture after the shot for 1-2 seconds. But if I look back/in the memory then the Camera tells me that there is an error.
If this has been true with several memory cards, which were formatted in the camera, then there's basically one last thing to try before you go for a replacement: turn off the camera, take the battery out, and leave the battery out for an hour or more. You might even recharge the battery while it's out.
If the problem continues when you put the battery back in and turn it on, then the camera almost certainly has a defect you can't fix, and you'll need to exchange it.
If it works correctly following the battery test, I would still test it quite a bit in the next week. Turn it off and on; download images. Remove/re-insert the battery. If it continues to work well, you may simply have found a bug in the firmware that will be identified and fixed later. If the problem recurs, then it goes back to Canon.