Comment 19 for bug 67130

The problem was still there with 6.10 final.
The point is that there is already a pation schema and the GParted is not able to handle it. Possibly only with a reiserfs root patition.
You simply go back to the user creation and open a new terminal window.
Become root and delete the partition table with fdisk.
Then you switch back to the installation script and ask to modify the partition table.