This is a very mysterious problem as in it was originally seen in the Storm and a few Tour owners are having this issue. I have not found anyone with an answer or heard of how to fix it. Reloading the OS and battery pulls do nothing to help it also.
Everyone that has had this issue has returned their phone. Sorry I cant be of more help on this one.
I just bought a Blackberry Storm this past week and at first had no issue using the Camera or the Video camera features until today. I had the very same message that you received " Camera won't start please close other applications and try again"
I tried a number of different attempted fixes that failed until........ I deleted the "7 Digital Music store app" that I downloaded yesterday. Whether that is or is not the reason that my camera and video camera wouldn't start is irrelevant to me as they now work since I removed THAT app........ Coincidence?