Problem with gparted

[Joep L. Blom]

I hope somebody can help me with a partition problem.
I have a new disk (1TB) and when I installed the OS (xubuntu 11.10) made 
1 primary and 1 extended partition, the latter with 2 logical 
partitions. The extended partition contains 2 logical partitions and a 
swap partition. Approx. 550 GB is free.
I want to make 2 extra logical partitions and use gparted from a Live CD 
(actually USB-stick).
Gparted works as expected except that it don't want to create a logical 
partition. That choice is greyed out. I can only choose to create a 
primary partition.
I haven all partitions on that disk - that were mounted automatically - 
unmounted but still gparted refuses to let me create a logical partition.
What have I overlooked? I need those partitions to copy to small disks - 
which are in that case - to the 1 TB disk to remove them from the case.
I hope somebody, more experienced with partitions than I am, can explain 
what I have to do to let gparted work as expected.
Thanks in advance,
Joep