In my design,I found that manufacturing grid was 0.01um, therefore all edges/corners of paths with dimensions in the range e.g 123.444 or 3.456 (3 digits after the decimal) were giving offgrid errors. A simple and easy way to deal with offgrid errors is to select the path or shape that is giving offgrid errors...then go to
Edit ---> Others---> Convert to Polygon
This will convert your path to polygon....(Converting your path to polygon doesnt alter your design.....And I think it that this method will work well if you convert any other shape to polygon)
Now if you select your polygon and look at its properties you will see all the co ordinates of corners of your polygon. You simply delete the third digit after the decmial e.g 123.444 will turn 123.44 (third digit removed).
This will not modify the shape of your path too much as it is the third digit dimension and will easily remove off grid errors.