unknown partition table error

I'm testing installs on a Dell 1750 server no raid, single hard drive. About 1 in 5 times I'm getting an error while attempting to format the swap partition indicating that the installer can't format the partition. When I Hit alt+F4, I see an errorindicating "sda: unknown partition table". If I reboot, 95% of the time the system formats installs fine. Any ideas what might be going on? Thanks