your installation medium is on dev/sdb1. You will not be able to create, delete, or resize partitions on this disk, but you may be able to install to existing partitions there.
I have gotten the above message while trying to install Ubuntu. I am reinstalling Ubuntu because of a crash that rendered me unable to boot Ubuntu so I decided to restart the reinstallation process only days after installing for the first time. This message appeared after I tried to change dev/sdb1 fat32 to ext2 in order to install Ubuntu to that partition. After I got this message I tried to select dev/sdb1 and press change but nothing happens no matter how long I wait for a response. I can’t format to fat32 as no root file system is defined. It tells me to correct this from the partitioning menu. To be honest, I am completely new to Ubuntu and have no idea how to proceed at this point. I can’t install Ubuntu and can’t click change on dev/sdb1 fat32. Maybe I should try to completely wipe my disk clean? If needed I am able to access the terminal by entering try Ubuntu. Any help at all would be appreciated, thanks :)