If you are trying to link a new device to the ISY994 and get a message 'Cannot Determine Insteon Engine' or similar, please check the firmware on your ISY994 to ensure it is the most current. You can find the most current firmware on the Universal Device's forums here. If in doubt about device support you can also contact Universal Devices' tech support to verify if you need to update your firmware or check your log files to determine the issue.
This message could also be caused by communication issues so you may wish to try moving the device to another location to see if there is any change.
For diagnostics, you can follow the procedure below with your ISY.
When learning the device, open the event viewer. tools>diagnostics>event viewer and then set to level 3
You should see this in the viewer:
If you don't see INST SRX after the first two then the device trying to be learned in isn't responding which results in a can't determine engine notice