We came across this issue today, where we were unable to access a Servers ILO due to someone leaving the remote console session open.
The following error was displayed
Remote Console is unavailable. It is already in use by a different client
We needed to access the servers ILO pretty quickly, so we had to end the other users ILO remote control session.
To do this do the following.
1, Go to System Status on the homepage and select diagnostics
2, Now press reset which will reset all connections to the ILO and then enable you to access the remote console on the ILO