Marketo times out after 4 hours of inactivity. A time out immediately after login is likely to be caching problem.
I also use Chrome 31 on Mac OS X:
Google Chrome 31.0.1650.57 (Official Build 235101)
OS Mac OS X
Blink 537.36 (@161986)
JavaScript V8 3.21.18.7
Flash 11.9.900.152
User Agent Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/31.0.1650.57 Safari/537.36
Please logout Marketo, select Settings - Advanced - Clear browsing Data and then retry.