Ok here is the file - sorry it is so massive! Not too sure why it is such a large file size, the 2 jpegs are only about 1mb each so its not that? I have tried the chamfer in a new file and it works just as expected. I opened up the file i was having the problem with, drew the line (simple polyline) did the chamfer and it worked! Then tried it again exactly the same and its back to not working. Which seems very odd. Another thing to note with this file (and another one that i did that had a similar roof profile) is that the roof is a sweep with 2 profiles and a single rail, this took about a minute to calculate on a 2.5ghz quad core machine which seems quite a long time. I have saved the file and when i have come to open it you should notice that the sweep has holes in it that weren't there when it was originally created - I have also tried this again this morning and the same thing happened. Why is this and why does moi generate a large file that becomes sluggish to work with when that sweep object (which isn't overly complicated) is turned on? I have tried disabling history for that object and turning off hidden lines but neither of which helped much.

Many thanks for looking into this
Rob

P.S. the plan jpeg is an old drawing thats why the building doesn't line up with the model - architects!!!