as was pointed out to me by three Wing Helper users today, it is important not to install the 1.6.0 Beta 3 into the same directory where the 1.5.0 is installed. In other words: please do not install 1.6.0 Beta 3 "over" the 1.5.0. Doing so will most probably result in Wing Helper not starting.
If you already are experiencing this problem, the solution is easy: just uninstall both 1.5.0 and 1.6.0 Beta 3, and then install again the version you wish to have. You can of course also have both versions installed at the same time and use them in parallel, but it is important to install them in separate directories.
Many thanks to all who pointed out the issue - that's exactly what I was hoping to learn from the Beta Test phase!