Weird G code problem

I wrote a routine to make part A. And it works fine. I then made a copy changed
a few things to make part B very similar to part A.

When I run the code for part B I get joint fallowing errors the thing that is most
puzzling is it happens in code That is a direct copy of code for part A.

So I recopied the block of code from A to B now it runs! Despite having made a
close examination of the code I could not find any difference or errors.

What could cause this ?

The joint following error is a result of the machine not being able to accomplish the movement desired (following error). It is not directly related with the code, although your different code may push the machine to move faster or in a part of the table where is more difficult to move the machine, so a error can appear.
Basically if the mechanics are ok, and the settings are ok (following error limit match your hardware), any code will not trigger the following error.