Err 91 Message - Canon Rebel

I have been experiencing an Err 91 message on my LCD screen. In doing research one fix was to remove the lens and clean the area carefully with an eraser. Do you have any other suggestions or causes for this error message? To clear the message I have to turn off the camera and turn it back on and hope it works.

Frustrated Photographer
Sara

I only had that message once... and it was the first time I used it at home.
I disconnected the lens, cleaned all the contacts, removed the battery and memory card... and started over.

Hope you figure it out.