This might be related,
if you have Exchange password issues, try resetting the iPhone by holding home + power until the apple logo appears; this takes about half a minute, you will see the shut-down slider appear, then the device will shut itself off, then it will restart and the apple logo appears. This is safe and will not delete any of your data nor settings.
I have 4 accounts, one iCloud, two Exchange accounts of which one is for GMail and the other for a corporate Exchange account, and one for a google calendar.
When I change my Windows password (AD domain account password), the iPhone promptly requests me for a new password, which I give and the iPhone will happily continue to fetch new emails. Until a few hours pass, after which it will receive no more email. When trying to update that Exchange account, either it will try to update "forever" or sometimes give a pop-up "Cannot Get Mail - The connection to the server failed"
This has happened multiple times after a password change. First time around I didn't get exchange email to my iPhone for about a week and much fiddling was done all over the place, passwords were changed on both Windows and in the iPhone, at some point after resetting the device the account worked again.
Today I had the same issue, I changed my windows password, entered the new password into my iPhone when it requested for it, mail continued to work until late evening when it stopped to receive updates. This time the only thing we tried to do to resolve the issue was restart the phone, which did not help, and resetting the phone, which resolved the issue (I've also sent a bug report to Apple)