HI Javi

Bad checksum errors in internal ram reported during startup imply a
corruption of the data stored in the User Preset and Setup memory. In
most cases this data corruption will not cause a problem and the error
can be cured by SETUP/Utility/fix. Serious corruption will require reformatting of this ram, with the total loss of all User Presets and Setup information.

If
this problem occurs more than very rarely, it may be a sign that the
backup battery for the internal memory is failing. This battery
normally has a life of around 5 years. 

Please try a Clear Setup first as this is required after OS update, then proceed to Fixinternal RAM.

kind regards

I