I have the MRX-500 latest software V 50.25 and MM 1.1.0 . When I press the Internet Radio selection from the menu it can take 5+ seconds or much longer to display the next screen selection. Also many times I get the "Unable to log on" error message. Somtimes the only way to get past this is to turn off the system then power it back up several times then it will work. Other times no amount of on/off cycles will correct it so then I forget about it that day. The other problem is an error of "Unable to play" even though it just played the same station fine before, it now refuses. When other stations are selected that worked the day before, they also refuse to play!
The MM V 1.1.0 has not been updated for a long time so I don't know if they will do anything about these issues.