Continuous interval shooting stops after 7th exposure?

I have a Nikon D5000, and recently I've been using this with my 18-55mm and 50mm 1.4g to take star trail and timelapse photos. I've been using the interval shooting setting in my camera and shooting in RAW.
Last night with my first attempt, I used my 50mm, set to f2.8, ISO 320 with an exposure time of 30 secs. The number of intervals was set to 100, with an interval of 2 seconds between each exposure. When I start the shoot, everything goes fine until about 7 or 8 exposures and then my camera stops taking photos. Although after this shoot, I realised that long exposure noise reduction was set OFF but high ISO noise reduction set to ON.
So my second attempt I decided to use my 18-55mm lens at 18mm, f3.5, 320 ISO, 30 sec exposure time and with the same interval shooting settings except changed the number of intervals to 200 (decided I wanted to take more photos.Am I right in saying that the number of intervals is around the number of shots your camera will take?) I also checked that long exposure noise reduction was off and the same for high iso noise reduction. This time I started the shoot and waited, and it continued to shoot to the 10th exposure so I thought I would leave it and come back a bit later to see if it was still shooting. I came back about 20 minutes later and my camera had once again stopped taking photos. Also I should mention that I did have my camera set to continuous shooting mode. And battery was fine, still had 2 bars after shooting.
Anyone know what could be the problem?

I had a similar problem with my Pentax. It turned out to be related to the memory usage. Luckily, my solution was an adapter that allowed me to connect to an external drive (i.e. My laptop) and I was able to get several hours recorded. Now I don't know that if this is your problem, but should be able to find a forum for your camera and get some good answers.

The camera could be overheating and shutting down.

Turn off the continuous mode. With an internal intervalometer, you may not need to worry about it, but if you were using a 3rd party external intervalometer, it certainly would matter.

I have a Nikon P7000 with a built-in intervalometer. It will only go a max of 30 seconds. If I force it to go faster - say 8 seconds with an external intervalometer - it will overheat and shut down after about 15 minutes.

Also if you are shooting intervals, you can reduce the quality of the photos to JPG-basic. Fact is, time-lapse; like any video, does not require the resolution that stills do, and reducing the photo quality will reduce the overheating. RAW is going to certainly overheat the camera after awhile.

Also, high ISO noise reduction will tend to overheat the camera too. You should not need it at ISO 320.

There are many reasons for this.

* Your camera buffer is finite, so once you fill it, you have to wait for the image files to write to your memory card
* Memory cards are rated by how fast they can read/write, in the case of SD cards, Class 10 is the fastest card available
* How large your image files determine how many continuous shots you can take before filling the cameras buffer.
* NR is an in-camera processing feature which can also cause a slowdown when image files are being written to the memory card.
* When using an interval timer, you have to make sure that the time between exposures exposures that you can take 30 second exposures and still have time for that image to write to your memory card.

It seems that you are pushing your camera beyond its design limits.

Try using a Class 10 card and setting the interval timer so that it takes one shot every two minutes. That should give the camera enough time to write to the memory card

Supposedly you have to set the interval to equal your exposure time plus at least a couple of seconds for the camera to process the picture. In other words, for a 15-second photo, the interval would be 17 seconds. But you have to test it to make sure you're leaving enough time for the camera processing to take place.