Ive got the same problem with my speaker system. Have been recommended to do the following:

1. unplug all speakers
2. Turn system on and volume up half way
(If it shuts off then blast yamaha)
3. Plug in Front speakers only and turn volume up half way
4. Repeate for centre speakers, subwoofer, and surround speakers.

This wont solve the problem but might isolate the dodgy wire/speaker.
Cheers!

Exact Same problem here too! Running a Yamaha RX-V630. Worked for 3 years with absolutely no problems and then suddenly it comes up with the dreaded "CHECK SP WIRES". The system runs a Bose Lifestyle speaker system. Just to make sure it wasn't the speakers, I hooked it up to Wharfdale (sp?) at a mates place (with his working amps wires). Even running stereo it cuts out!....Also, volume really doesn't seem to matter....If anyone has a fix it would be much appreciated. I have cleaned the system inside out- so eliminate dust. I have also checked most components and they seem to be fine!!!

Dear,
There are some chances in YAMAHA recievers behaving like this.
01.You speaker may be rated 4ohms.But impedece setting on back of your reciever is set to 8ohms.This will lead to overcurrent flowing through ur reciever out put which will automatcaly act the protection relay in the reciever to switch off the reciever.
Remeady.Switch of the reciever and change the impedece setting.Never do it while reciever is SWITCHED ON
02.Any of the speaker wires shorted .Check the wires.
03.Over heating due to improper ventilation
Regards,
RAJAGOPAL

Did Yamaha ever have a fix for your speaker wire message? If so, what was it? I'm having the same issue with my RXV-1600.

your amp can't cope with your speakers i have the same problem when i wire in the hfe of my rel quake it cuts out as soon as i disconnect it there is no problem

I have the same fu**ing problem with my rx-v450   yamaha sux "check sp wires"

If you are still having this problem (I know it's been a while), I hope I can help.  I had the EXACT symptoms (can't be sure the problem is the same, though).  I contacted Yamaha, who advised that the unit requires servicing.  I was disappointed, as I didn't want to do without the receiver.  So, I contacted a technical friend who I believe to know everything electronic.Without mentioning the CHECK SP WIRES error to him (I just told him about the automatic shutoff), he suggested to me that it may not be my receiver at fault.... it may be a speaker going bad and drawing too much current.  Immediately, this struck a chord with me, as I know I was getting that error.  In fact, he suggested it may be my center channel, as that is usually the culprit (he never even saw my setup).  Turns out, he was right.What I did, was to take out the center channel and turn the volume up to where I know it would shut off.  It did not.  When I put it back in, it shut off at the volume.  I then used a different center speaker and "voilà", the system no longer shuts off... (you can also check this link for suggestions on how to check the speakers http://www.yamaha.com/yec/faq/faqdetail.html?CNTID=205015&CTID=5009150#t_205015)

Please let me know if this helps.

Hey count me in.  I've got the same problem with an RX-V2500 and an incredibly stupid twist.  The receiver only shuts down when playing a CD (Yamah CDC-585).  I've been through all the tests.  Can't find a maverick speaker wire.  I've ordered a replacement receiver and will report back.  Also plan to uninstall the entire system  (in-ceiling speakers, zn. 2 imp. matching vol controls- the works).  We're gonna ohm out everything...and finnaly put this issue to rest.

same problem with the yamaha amp CHECK SP WIRES. The hell with it I have tried everything. You can't win, ya just can't. I am utterly disgusted with yamaha at this point. I thought There was only a few of us out there with a faulty amp but I have already had 2 back to back do the same thing. HTR 5950. But like a great philosopher once said just through it in the gutter and go buy another.