IPSEC tunnel issues

I have had a IPSEC tunnel up for a couple of years. Then this morning out of the blue it is down, saying phase1 negotiation failed due to uptime. I have gone through the config over and over, reconfigured with the same results. Any suggestions or ideas?? Thanks!

Downgraded both to 6.33, still no issue. Then upgraded both to 6.37.1 and the tunnel is up!