error "illegal software format" in upgrade fw .ros file of Cisco Sg200-26 small business smart switch

Solution 1:

immediate upgrade to the latest firmware was not possible. an intermediate upgrade to newer bootloader 1.3.5, followed by an upgrade to firmware version 1.3.7 needs be completed prior to upgrading to latest firmware v1.4.0.88.

Solution 2:

I had boot loader 1.1.06 with firmware 1.3.0.62 and I was getting the same errors when trying to upgrade to 1.4.0.88.

I used sx200_boot-13506.rfb to upgrade the boot loader to 1.3.5.06.

Then I had to upgrade the firmware using sx200_fw-13558.ros first to 1.3.5.58. Then I was able to finish the upgrade with sx200_fw-14088.ros to 1.4.0.88.