Problem regarding Upgrading Hard disk fr

I have Disk0 into my system and using windows 2000 server. i have one primary partition and a Extended partition which contains 2 logical drives. I have deleted one of the logical drives. it appears in disk management as free space of 1GB but when iwant to upgrade my this basic disk to dynamic disk it shows an error message that it require at least 1MB free space for this purpose.However there is a free space of 1GB after deleting Ligical Drive. Pls help my to diagonse this problem.