BootROM: Image checksum verification FAILED in fortigate 30E

i have a fortigate 30E series; I'm getting the error below and i'm not able to enter the configuration menu to install a new firmware. Can someone please advice on this issue thanks.

BootROM - 1.73 Booting from SPI flash BootROM: Image checksum verification FAILED BootROM: Bad header at offset D4200000 BootROM: Bad header at offset D4400000 BootROM: Bad header at offset D4600000 BootROM: Bad header at offset D4800000 BootROM: Bad header at offset D4A00000 BootROM: Bad header at offset D4C00000 BootROM: Bad header at offset D4E00000

Trying Uart