Help - 5d2 error 70

I recently went to shoot birds with a 5D2 500/4 setup.

Unfortunately after a while it started raining like crazy and there was no shelter at all except some small trees.

Despite my best effort the camera was completely wet and for a day it just refused to focus at all. The water even creeped into the LCD.

After that I was able to use it again and there is an Error 70 every second time I use it.

It reads "Error 70: Shooting is not possible. Turn the power switch to and again or re-install the battery".

Strangely, it appears precisely every second time. That is, when I turn it off and on again, it started to work. And the next time the error msg appears again.

I researched a little bit here but the none of symptoms relate to mine.

Before I send it off to repair, I thought I would check here. Any advice would be welcome!!