Thanks for pointing out this problem. I posted a new version 2.5.7 (build 543) that resolves this issue. Please download the latest version and try again. Also, please note that the 64-bit version now requires MCR2016b (9.1).
OpenSees Navigator only recognized OpenSees.exe or OpenSeesSP.exe executables, so if you used any OpenSees executable with a different name you got the error message that the executable is not supported.