Apline mrv-f345 error

I am trying to re-tune theis 4 channel, It was set-up about a month ago and has worked flawless until the customer let his friend adjust it. Now when played at 80-90% volume it says cur and shuts down. It comes back on when the stereo is turned off and back on. I do not have the install manuals. I am sure someone on this forum can help. I have adjusted the gains back down both 1&2 and 3&4 are at 2.5. It sounds good/ no distortion at 90% volume but it goes into some kind of protection( I assume) after about 5 minutes of playing. It has all type r  speakers, seperates in the front and 6x8 in the rear. My last question is why do people have to tinker, when it already sounds great????? Thanx for any help.

dude, if I was to guess I'd say blown or goin' speaker. I got a manual at work, I'll check tomorrow for ya.My rifle is my friend...

Ya I started by only running one set at a time and his (used to be an installer) friend had the rear 6x8's trying to produce some very low notes, speakers were flopping like fish out of water. They sound like doodie even when adjusted properly. Its in his court now, I have the gain turned as low as it goes for the rear speakers as requested by the customer, stills goes into protect though. I suggest disconnect them unitl he gets new ones, but what do I know. I am sure his installer friend can fix the speakers just like he found all that hidden sound I missed:)