I am having the same issue. I originally installed a viewer on my PC to try it out, then when I tried to install the viewer on another PC I began to get this message. I was not even sure how the program worked at that point. Once I encountered the error, I then installed the USB key version of the viewer on that type of device. It worked fine in the original network it was installed in. In trying to use it on another network to connect remotely to my original network, I am getting this message. Error: Another user is using this copy of R-viewer. I used the remote utilities program to figure out what level of license to buy. I am the only operator who wants to use the program to connect, at different times between five computers. RU advised me to just get a free license. So, if I am able to use a free license to do this, why do I continue to have this problem. More importantly how do I fix it? Please let me know. Thank you.