If EventSentry reports "Access Denied" when trying to read data from the temperature and/or humidity environment sensor, then this usually means that another application running on this machine has exclusive access to the serial COM port the sensor is attached to. If another application is blocking the same COM port that EventSentry is using, then EventSentry is unable to open the port and thus read data from the sensor.
The EventSentry agent only opens and locks the COM port while it is actually reading data from the sensor, after which it disconnects and other processes could open the port and lock further access.
Please make sure that no other process on the server (e.g. UPS and similar software) is accessing the COM port you are using for EventSentry. See the links below for software that might help identify which process is using which port.