I also get this repeating error about the gameclient and stopping working.
What I've seen work: disabling (closing) x-fire. I've met other users that this has helped. Not everyone runs x-fire, though.
I've heard that Steam can be causing issues, as well, and heard it suggested that running the game outside of steam can help resolve this. I do not run the game through Steam, so I cannot comment on that one personally.
Lastly, on the game's launcher, there is an 'Options' link at the very top, while you're signing in. If you click on this, on the little pop-up page there is a text box for 'advanced options'. Inside the text area there, I have added "-console" (which is a sort of debug/data console). This option has allowed me to run x-fire at the same time, and eliminated 99.99999% of my crashes =)
I hope that this information can somehow help someone. I also hope that whatever happens because of this console being open, can be implemented to work even when it's not open :>
Using the -console option so far seems to have fixed the problem for me