I tested your save game 3 and ran it for 4 years and kept buying shares when any of the companies' shares diluted. But no problem has occurred.
1) Did the freezing problem occurred in your game immediately after you have pressed the [Buy] button or after some moments?
2) Did the freezing problem occurred in actions other than buying shares?
3) When you play a normal game without such extremely stock play, did the freezing problem occur?
4) Has any message window popped up when the problem occur? Could you please capture a screenshot when the freezing problem happen and post the screenshot here?