I had a problem weeks ago when upgrading Cisco ASA 5515-X Next Gen Firewall from version 8.6 to 9.1.3. The upgrade error I got was “No Cfg structure found in downloaded image file”. I checked the documentation and it says allowed to directly upgrade from 8.6 to 9.1.3. Searched over Cisco Bug toolkit and found a bug related to the issue I was having.
Bug ID and Title: CSCuh25271: Upgrade fails w/ msg “No Cfg structure found in downloaded image file.”
Symptom: Upgrade fails with error message “No Cfg structure found in downloaded image file.”
Conditions: Upgrade from version without fix for CSCua99091 (e.g. 9.1.1) to image with fix for CSCud21312 (e.g. 22.214.171.124).
Workaround: If the customer is running an image without the fix for CSCua99091 (e.g. 8.4.4, 9.1.1) then the customer needs to do an intermediate upgrade to a version that includes the fix for CSCua99091 (e.g. 8.4.6, 9.1.2) and then upgrade to the desired image (e.g. 126.96.36.199)