Hi,
I have also experience these errors when i use "path" to create 45deg-angles signal lines. Now to avoid this error, i just use "rectangle" and "polygon" to create the shapes. My minor grids are set to 0.01, so when i check the properties of the shape created and when the co-ordinates show 3 decimal places, there will be drc offgrid errors. However, if there are only 2 decimal places co-ordinates, then there will be no drc offgrid errors. Hope that this helps u to solve the problem.