That happen to me last year .I couldnt park at Signature so It was a very long stroll from MGM and I was 20 min late .In the end everyone was happy

First, I am jealous you went to that show...I was supposed to, but familial obligations kept me from going, so I had to give my tix away!  
I know it had to have been amazing....Sting and the Philharmonic Orchestra?!  Wow!  You are lucky!

Secondly, the security guard at the gate told me the same thing, and recommended parking at MGM and walking.....all that way in over 100 degree heat?!  No thanks....it's a shame...surely they must have some way of handling overflow valet parking....perhaps the economy and MGMs troubles are at play here....

I generally like that property and have never had an issue there....though I've received emails and PMs from Several others stating that they had the very same experience....it's too bad.

That's absolutely how things work out here in LV most times....however, my friend requested that I did not call or text his cell, so that left me with only the option of ringing him at the hotel.  

Unfortunately, the front desk failed to answer for either of us; he reported being on hold for over 15 minutes once they finally did answer...and, I was unaware of the inside walkway that connects MGM with Signature to gain access....and, we couldn't meet at the bar or lobby, as I could not get into valet...bummer all around!