swl_fix.iso
This is used if the unit is stuck with Gateway Error 202 or similar and is unable 
to boot after the upgrade. It’s based on the 272x firmware but can be used to recover 
RNS 510’s running any version. Insert the media into the RNS 510 and start a 
new SWL process by pressing Setup + Eject +Info/Mic (top right hand button next to the DVD slot). 
It will attempt to restore a new SWL process and will enable it to boot up. 
(Thanks again to Josi)