This code cannot be compiled with mono/master or mono/3.12, but can be compiled with mono 3.10:
The specific line (pasted here for convenience) is:
rc.DrawMultilineText(p0 + new ScreenVector(0, fontSize * 1.5), errorMessage, this.TextColor, fontSize: fontSize, dy: fontSize * 1.25);
and the compile error is:
PlotModel/PlotModel.Rendering.cs(214,140): error CS1525: Unexpected symbol `1.25'
This is probably a dupe
*** This bug has been marked as a duplicate of bug 24784 ***