Thanks, that is all great information. No absolutes in these situations but the UPS is a good place to start. I personally have had problems with mine until I put it on a FilterLinc and so have many others. You can find many references on the Smarthome forum. There is a recent case on this forum where multiple FilterLincs solved a powerline communication problem. The power supply in a UPS must filter the powerline so well that it attenuates the Insteon signals below the point of reliability. There are other appliances, laptops, TVs, cell phone battery charges, and others that can have the same affect. Some generate noise, some attenuate the powerline signals. FilterLincs address both issues. Easiest way to track these down is to unplug the devices, turning them off is not enough because many of these devices still have their power supplies active to respond to remote controls. You can try unplugging the UPS temporarily. Has to be unplugged, not just powered off. Another temporary test can be done by plugging the EZSrve into a good 50’/100′ 3 wire extension cord and plugging the extension cord into an outlet far away from the PC and UPS. This may bring back your problem of not being able to communicate with all your devices when you plugged EZSrve into a different outlet. This sounds like a separate problem perhaps with powerline coupling. Are you using Smarthomes SignaLinc RF couplers or the newer Access Points (Item #2443P) devices, one on each leg of the power line to couple the Insteon signals across the two legs of 120v power. The lack of one of these types of devices or them not being plugged into opposite legs of the powerline is often the cause of not being able to get to certain devices. If you find you do need FilterLincs (maybe more than one) they are Smarthome Item # 1626 for the 5 amp version (which I just noticed is on sale) or Item #1626-10 for the 10 amp version. Try unplugging things and moving the EZSrve plug point first but having a FilterLinc between the PC/UPS and the powerline is always a good idea. Just be sure that the EZSrve is not supplied by the UPS when all is done. I have heard of Insteon signals getting through a certain type of UPS but generally the EZSrve would be unreliable to completely unusable if powered by a UPS.
There is a Smarthome Device Manager (SDM) install that may help with the SHN Utility problem. It is available on the SHN Downloads section. The Utility can be a good diagnostic tool being another Insteon application if we can get it running. If not on the latest release, download and install the Utility Suite again also.
Keep us posted on your progress, please. thanks