I was checking the manual of proton+ and could see that that for OSC or Xtal, it is only possible to use 3,4,8,etc. MHz.
Yes it is 3-48MHZ but it all depends on what pic your using,
I would try it by myself but currently I still cannot download the cracked version from the link and the demo is said to support only 4 MHz and 20 MHz.
That's the demo vesrion, Not sure about cracked vesrion though