please have a look at this old thread:https://forum.ultravnc.net/viewtopic.php?f=67&t=29750&p=93579#p93579
This was the first time this error occured. And even that you did not answer my post, you fixed that bug in 1.1.7.
So, the best thing might be to have a look at the code changes between 1.1.6 RC and 1.1.7.
This monitor is a single ASUS PB278Q and it has a native resolution of 2560 x 1440 x. No second monitor is in use.
This error occurs with mirror driver enabled and disabled. There's no difference if you use it or not.
And it even does not matter what other graphics related settings you adjust in the ultravnc.ini. You will always get this error.
The only thing to work around this is to replace the ultravnc.exe 220.127.116.11 with the ultravnc.exe of your latest pusblished 18.104.22.168 release and restart the server service. After that you can use any 1.1.x viewer to successfully connect to that machine.
That's why I'm pretty sure there must be a code change between 22.214.171.124 and 126.96.36.199 that is causing this issue. Just ask yourself in which cases you throw that error message mentioned in my two postings.
I also tested FullHD screen resultion at 1920 x 1080. This is working fine using you latest 188.8.131.52 build. Perhaps some variables used might cause a kind of overflow if screen resolutions above FullHD are used. That could explain why ultranvnc thinks that a value for height or width is negative even that I cannot imagine of any data structur that causes overflows at values above e.g. 2048. You are surely using a some kind of integer for storing the values for height and width.
Only you will know