To improve security Ruckus introduced certificate sighed firmware image to prevent introducing a hacked version of code into the AP.
There are 3 types of firmware versions:
UI -Unsigned Image - original type without certificate signed
ISI - Intermediate signed certificate - a bridge between UI and FSI allowing upgrade or downgrade to either.
FSI - Fully Signed Certificate
The rules are you can only upgrade or downgrade from FSI to ISI or from UI to ISI
AP standalone code 100.x is UI code so you cannot download an FSI image.
Starting in version 104.x AP images are ISI.
So try using a newer version of AP code (104 or above)
To verify which type of AP firmware you have you can use the: fw show all
command from the AP CLI
ZD AP code 9.13. and Unleashed 200.2 introduced as ISI, either of these version can be used as bridges to newer FSI version of firmware or to go back to older UI versions of code.
This data should be available in the Release notes for each version
AP Image Signing
security by requiring verification of AP firmware images to ensure the
has not been modified and that the source code executed by the system is
authentic code provided by Ruckus Wireless.
I hope this helps you solve your problems.