drawing locks up in 1 drawing only

In 1 drawing I am working on,whenever I use the perpendicular osnap, the
drawing locks up and I have to close using control-alt-del. All the other
osnaps work fine. And it is only in this 1 drawing that there is a problem.
It locks up in moel space and paper space/layout tabs. I tried purge all to
get rid of anything not being used in drawing. Also tried audit and recover,
neither found any problems. I also tried starting a new drawing and copy and
paste the old drawing in, the problem came in with it.

Anyone have any ideas?

thanks
John Segaline

 

I am using aotocad map 2004 with windows xp pro. thank you, i will try
wblocking, the drawing is only about 1 meg.
John Seg.