737-300 FMC issue

[vin]

First of all thank you for this wonderful aircraft. For me is really the best: it's so real.

I have two issues with FMC during flight:

1. If I change something on FMC (flightplan) the aircraft crashes. It means i can't handle it all is blocked. This is not normal. Before crashing, to change something is very hard. I mean very slowly. After two or three times crashes and i'm not able to do nothing on aircraft.

2. I can't add an holding. i press the button hold, the new windows open but i can't add nothing.

Thank's.