On 3 august I installed DiskGenius (and Ext2Fsd; I did not use it) to access to linux partition from windows and everything worked well.
Yesterday (5 august) I used Ubuntu 20.04 and after I turned off my laptop (on it there is the dual boot Windows 10 + Ubuntu 20.04). I turned on my PC, I selected the windows option from the boot loader GNU GRUB (as usual), then I used only firefox in Windows. Finally I turned off the PC.
Today, when I pushed the power button, the following message appeared:
Unexpected return from initial read: Volume Corrupt, buffersize 0 Failed to load image \EFI\ubuntu\grubx64.efi: Volume Corrupt start_image() returned Volume Corrupt
and then the Windows 10 OS starts.
How could I fix this problem? I tried to unistall both Ext2Fsd and DiskGenius but the situation remained unchanged.
P.S.: yesterday linux downloaded and installed the last updates before I turned off it.