The project file could not be saved. Your system appears to be low on memory...

It's been a while since I have worked on a Storyline Project (my new job is using Captivate). From what I recall, I was usually having this problem while working on software simulations which had large video capture files.

I started making a habit of saving frequently and periodically closing and restarting storyline. This resolved the problem (although it was not very convenient).

You should probably try ensuring you have the most recent update like Ashley recommends.