[coLinux-users] build disk img help

[卍\(^o^)/卐 <gol...@qq...>]

Hello, I'm a new baby to coLinux. Thanks for your wonderful job!
 now, i have some trouble in creating disk image!
 here is my steps:
  
 first, I installed a xubuntu system in VirtualBox(my host OS is Windows7)
 second, I turn off the Virtual machine, using VBoxManage.exe covert the "vdi" disk file to RAW format
 third, I use dd coverting the RAW image with para "bs=512 skip=63"
  
 could you tell me whether these steps has something wrong? And How to make rootfs image?
  
 wish to hear from you !
  
 Happy new year!
  
 Err info:
 VFS: Mounted root (ext2 filesystem) on device1:0.                                                                                                              ===========================================================================     # This process will install (if necessary) the coLinux modules for the          # coLinux kernel.                                                               input: AT Translated Set 2 keyboard as /devices/serio0/input/input0             ===========================================================================                                                                                     Determining /, Found.                                                           Mounting /                                                                      EXT3-fs (cobd0): error: can't find ext3 filesystem on dev cobd0.                EXT2-fs (cobd0): error: can't find an ext2 filesystem on dev cobd0.             EXT4-fs (cobd0): VFS: Can't find ext4 filesystem                                ISOFS: Unable to identify CD-ROM format.                                        mount: Mounting /dev/cobd0 on /mnt/linux failed: Invalid argument               List of all partitions:                                                         7500         4194272 cobd0 (driver?)                                            No filesystem could mount root, tried:  ext3 ext2 ext4 iso9660                  Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(117,0)Pid: 1, comm: swapper Not tainted 2.6.33.5-co-0.7.8 #1                          Call Trace:                                            
 [<c122f6af>] ? printk+0x18/0x21                                                 [<c122f681>] panic+0x4e/0x64                                                    [<c12eea9c>] mount_block_root+0x242/0x254                                       [<c108dac7>] ? sys_mknod+0x27/0x30                                              [<c12ee0c7>] ? kernel_init+0x0/0xea                                             [<c12eeb07>] mount_root+0x59/0x5f                                               [<c12ef66f>] initrd_load+0x277/0x38c                                            [<c12ee0c7>] ? kernel_init+0x0/0xea                                             [<c12eebcb>] prepare_namespace+0xbe/0x183                                       [<c1080d40>] ? sys_access+0x20/0x30   
  
 thanks