Uptime Infrastructure Monitor cannot monitor an ESXi 3.5 U4 or higher system (including 4.x) unless it is connected to Virtual Center. VMware has added access restrictions to its API to prevent data collection from ESXi systems that are not connected to vCenter. Because Uptime Infrastructure Monitor needs this data for monitoring, an error will display in the UI indicating that Uptime Infrastructure Monitor is unable to retrieve configuration information.
The log file will also show a stack trace with the following line:
fault.restrictedversion.summary
This is not an issue for ESXi systems running version 3.5 U3 and lower.