I was forced to use 1872 for one part last week due to an enhancment i needed with guided curve. i recieved the same error, but was lucky enough to have saved many revisions along the way so i did not loose anything. We used to move to major releases as they came out. getting new featutes is a big plus for us, but its become to much work to update all of the individual tool paths, methods, intalled machines ect for how often the new format is changing. We are probably going to stay with 12 for a while.