SOS_Installer Ubuntu 9.04_Unmount partitions that are in use

[cl8588]

Hello,everyone.
At disk drive installer ubuntu 9.04 had a error info:
================================
Unmount partitions that are in use?
The installer has detected that the following disks have mounted partition:
/dev/sda
Do you want the installer to try to unmount the partitions on these disks before counting?If you leave them mounted,you will not be able to create,delete,or resize partitions on these disks,but you may be able to install to existing partitions there.
================================

Why???
SOS!!!!!!!!!
PS: I'm so sorry,my English is not well,and on the live CD to internet,no chinese input.
Pictures:

[smallapple]

硬盘安装都这样，点“否”，然后按 Ctrl+Alt+F2，输入 sudo umount -l /isodevice，按Ctrl+Alt+F7返回再继续下一步

[adagio]

硬盘安装都这样，点“否”，然后按 Ctrl+Alt+F2，输入 sudo umount -l /isodevice，按Ctrl+Alt+F7返回再继续下一步

额……，我点“是”，然后就可以装了，不过我是多硬盘

[smallapple]

代码： 全选

额……，我点“是”，然后就可以装了，不过我是多硬盘

我试过了一次，不能保存分区
也许我比较背？

[cl8588]

硬盘安装都这样，点“否”，然后按 Ctrl+Alt+F2，输入 sudo umount -l /isodevice，按Ctrl+Alt+F7返回再继续下一步

Thank you so much.It's well,and is installer now...

[hcym]

应该点“是”吧，我都是单硬盘安装

否则装grub又麻烦啦

[smallapple]

看来真是我比较bei

[cl8588]

我这里也是，若不按照smallapple兄弟的指点，输入“sudo umount -l /isodevice”，执行“是”或“否”均无用处。。