Q:

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

I own 2 cisco switches small business switches.
they are both SG200-26 26-port  gigabit smart switches. One has fw ver. 1.0.0.19 , while the other has version 1.1.1.8. 
I am now trying to upgrade their firmware to the latest version 1.4.0.88, found here http://software.cisco.com/download/release.html?mdfid=283771818&flowid=24301&softwareid=282463182&release=1.4.0.88&relind=AVAILABLE&rellifecycle=&reltype=latest
I go the http management interface from google chrome and select "upgrade firmware from http". I choose the .ros file and try to carry out the update. 
Unfortunately, the system informs me that the copy has failed and that the software is of "illegal format". 
I have double checked that the file is the correct one. what could be wrong? Do I need to update the bootloader first? is there a guide for that? 

A:

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.

A:

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.

