On my old camera I used to get a bunch of ERR99 popups all the time to the point where I was going to send it into Canon service to see what was wrong with it.
Before I did that though I went onto google and tried to find the root cause. ERR99 is really a general code so I couldn't find the exact cause but after reading a page about using a pencil eraser to gently clean the contacts of the camera/lens connection .. the ERR99 stopped!
Keeping a pencil in the bag is a good idea anyways but now it serves dual purpose.
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