This could be a few different problems. First, make sure that the battery is inserted correctly, and that the battery cover is closed correctly. If you are still experiencing problems, please head over to the troubleshooting page here.
This is a known error with the Canon PowerShot S100 camera. For more information, you can visit Canon's press release here or you can attempt to fix it here. Here is a link to our troubleshooting section about this issue.