Aogee Alta E47 trouble

[LSPD]

Hi there,

After several months of trouble-free operation, I cooled My Apogee Alta E47 camera to -25 C and it produced this image yesterday. In the past weeks it was running at -15, -20C because the nights were very warm. The pattern is similar regardless of whether the CCD is cooled and also largely independent of exposure. All pixel values are close to 65000.
Does anyone have an insight into what might be going on?

I'd apprecite any help.

Laszlo