Please use the CLI to upgrade, it'll give you exact error where the problem is. Copy/paste the error here.
Exacute following command from CLI
For ERLite-3 and ERPoe-5
add system image http://dl.ubnt.com/firmwares/edgemax/v1.9.1/ER-e100.v1.9.1.4939093.tar
For ER-X and ER-X-SFP
add system image http://dl.ubnt.com/firmwares/edgemax/v1.9.1/ER-e50.v1.9.1.4939092.tar
