Comment 22 for bug 464411

@mindseye1: First, you should run "sudo blkid -p /dev/sda1" and make sure it returns "/dev/sda1: ambivalent result (probably more filesystems on the device)" (substitute sda1 by your missing partition)

This means that there is a vfat header in the first block (512 bytes) of the partition and an ext2/3 header in the following blocks.

Next, you should make a full and verified backup of your partition, in case anything goes wrong (e.g. by mounting with an old live-CD).

Last, "sudo dd bs=512 count=1 if=/dev/zero of=/dev/sda1" zeros the first block, thus removing the vfat header. Note the MBR will be unaffected by this.

It is generally a good idea to read the manpages of the commands you are told to execute (e.g. "man dd").