You should never see this message under normal circumstance.
One way that this message can occur is if more than one partition is set "active" or bootable; only one is allowed to be at a time.
It is possible that the master partition table has become corrupted.
The standard DOS and Windows disk utilities will not allow you to set more than one partition active.
If you are using any funky utilities to manipulate the partitions, for example in a multiple-operating-system environment, run the fdisk dos utility from a floppy disk and make sure only one partition is set active.
Partition it with 8.0, then sneak it into the 8.1... does that work?