Timer5 is not busy , but still unable to open PWM ch10-12 . . .
My board uses 9 PWM channels , and i could use Timer4 but i also need 1Wire so i can't spare the I/O Timer . . .
I believe that I found the problem and fixed it but we haven't tested it extensively. You can try the experimental version of the ZBasic Library code for the mega2560 that is in the attached .zip file.
To use it, first rename the existing libmega2560.a file in the zlib/avr/lib subdirectory of the ZBasic installation directory and then copy the same-named file from the .zip file to that directory.