The thing about the UC540 is that while Cisco will only support units installed/maintained by CCA, a great many installers use the command-line interface. And it is my understanding that once someone has started making changes outside of CCA, using CCA can cause problems.

If CCA previously allowed you to make changes to the UC540, but now says it is unsupported, making sure you're on the latest CCA (just in case you're using a different PC/install of CCA this time around), and if that still doesn't work I'd suggest power-cycling the UC540 and trying again.