quicktime player refuses to save video screen

Hello. I have two problems with my quick time screen saving:

1. there seems to be a limit in the amount of time i can make a movie screen recording because Quicktime stops recording by itself after some minutes. Is this expected???
2. most of the screen recordings i make cannot be saved afterwords. Quicktime just states some warning like “it was not possible to save”. Although i can see the entire movie captured it does not let me save it for some choose destination (???)

I’m doing this on a iMac 2.9 GHz Intel Core i5 with 8GB 1600 MHz DDR3

Operating system is OS X 10.9.5

Quicktime player version 10.3 (727.4)

Help please!!!

Pedro