I don't understand g-code that well, but I'll tell you what I know!
Firstly, you cannot have 2 g's on the same line, so you will have to seperate G20 and G90.
Secondly, I have just looked through the turbocnc manual, and it does not mention M98 and M99. In the turbocnc example (sample.cnc) the writer uses M60 and M62 to call sub-routines, so maybe this should be used instead.
Like I said, I do not know g-code, I have only read the instructions!