The missions in S. T. A. L. K. E. R. _S.N.I.P.E.R. (S.T.A.L.K.E.R.: Call of Pripyat)

Guys I have a problem. I recently started playing S. T. A. L. K. E. R. _S.N.I.P.E.R. (from the series Call of Pripyat), I was constantly off during transport from one location to another (I mean from one card to another), sometimes on open ground crashes, and sometimes when saving the game crashes. Help to solve this problem.