Why this happen each and everytime when i open the model and make any changes than programme is crashed.
Try to rename folder STAAD.Pro CONNECT Edition into STAAD.Pro CONNECT Edition _1 in the folder C:\Users\User_Name\AppData\Local\Bentley\Engineering\
If that does not help, copy STAAD.Pro model (.std file only) into a new folder and try to run the model from there.
Also, make sure that you run the model from the local hard disk, not from the network drive.