Error 99 can be caused by several different problems that effect communications within the camera, problems with the shutter or aperture, etc. It's a generic "Houston, we have a problem" code. Dirty contacts in the lens mount and dirty battery contacts are fairly common causes. So, you easily sort your trouble out. But in case the issue is related to loss or deletion of photos from the camera then there is one way out i.e.
photo recovery software which is the best way to get rid of this issue.
All the best!