Don't get panic when you see this thing, and also don't consult customer care or some other repair shop to waste some bucks. Usually this error will be found when you made a unsuccessful attempt of dual booting your Mac with Windows. To fix this error, restart your Mac and hold down option key, after hearing chime on booting. If you don't want to install windows, then select the Mac Recovery partition. Then from the menu on the top, select the boot disk option and select the drive in which Mac is present. Restart and enjoy... If you wish to install Windows, then insert bootable disk and select the Windows partition that you had created using boot camp, and proceed with installation. In both cases you will be able to boot normally.