Ethernet Shield stops working after 24h?

I created a door alarm using my Arduino, and it works fine. It beeps a piezo when a door is opened. It also hits a local webserver with the door pin that was opened (which sends an email).

The problem is that after a number of hours, it stops hitting the webserver and thus emails don't go out. It still makes the sound (and blinks a LED) so I know it isn't hanging or anything, and since it takes so darn long to stop working it is hard to debug. I just know that the next day it isn't sending emails anymore. I can hit the reset button or power cycle it and it will work fine. Any ideas?

Here's my original project:

Posts on my blog about the project (with code):

There is a workaround fix at Reply #16 of

Excellent thank you. Also the 0013 release notes seem to indicate this fix might be in there (I was using 0012).