VPN IPSec Errors

We have some Balance 20’s and 580’s linked into Windstream’s MPLS infrastructure via IPSec tunnels and the event logs are filling up with IPSec errors. I’ve verified all the settings and timers, and the tunnels seem to be staying up (with some occasional exceptions), but I cannot determine why these errors keep appearing, and so frequently. The tunnels are configured for Main Mode using a preshared key.

Also, sometimes the InControl Event Logs seem to show things the Peplink IPSec Event logs don’t even show.

The errors are “No acceptable response, please verify the settings” and “IKE Proposal refused, please verify Phase 1 (IKE) settings.”

This may cause by either IPSec peer keeps proposing invalid proposal or IPSec connection attempt from unauthorized source. Please help to open ticket if you need to confirm further.