Ignore JuhaEdag's comment, CATIA can break off and stop for a whole number of reasons, legal copy or not.
If it does this very often verify that your computer setup is up to code and everything you have is properly certified by Dassault. You can check on their site for you grafic card and memory and whatnot.
Other than that, it can be a problem of need of memory, a problem with your pieces, between other reasons.
If all else fails, call Dassault's assistance, or your local reseller.