Caine Linux v10 installation gives error: Operation not permitted during write on /dev/sda

I'm trying to install Caine Linux. I downloaded ISO from https://www.caine-live.net/ and "burned" it with Rufus to a memory stick. Then I bootet from this memory stick to Caine Live. In Caine Linux I made disks writeable by clicking the harddisk icon on the status bar -> then click Install 18.04 on desktop. On installation type I selected "Erase disk and install 18.04" Here I got the error "Operation not permitted during write on /dev/sda". Any suggestions?