Esxi - Configuration Rescanning Failed.

I have 12 ESXi servers being monitored in UpTime (v.5.2.107). All but three seem to have disconnected and I can no longer rescan them: Configuration rescanning failed.

If I removed them and try to re-add them, it fails and I cannot add them back.

I have tried rebooting the ESXi box, still fails. I have verified 443 is open between the servers via telnet. I have verified I can hit the ESXi SOAP interface from the UpTime server, still fails. I have verified CIM is enabled.

Any ideas?

Uptime: Version: 5.2.107
ESXi Version: 3.5 Update 5

Thank you,
Andy