I have a Mint.com account and some of my accounts that used to work no longer work properly. I am confident that I'm putting in the proper information that it asks for but I'm still not having luck. Are there steps I can use to troubleshoot this issue beyond the very basic "double check that your credentials are correct?"
I've noticed what you're describing as well. At least with some sites, if they provide two-factor authentication, they ask you to verify factors beyond username/password from time-to-time. Generally, I've been able to resolve this by going to the site manually to verify my additional factors. Then when I refresh, the information updates again.
Two-factor security seems to be more and more prevalent with banking sites. I know Citibank does it for their student loan website. Vanguard does it for their site as well. Chevy Chase Bank (now owned by Capital One) does it on their website too, but I haven't had any update problems on that account with mint.com.
I assume you've already checked your account number and other obvious stuff. Mint.com uses the same kind of system as Quicken and other financial tools to allow those tools to get your account information. I would contact your bank to ensure that your account is currently configured to allow that access. Some banks require you to request it, otherwise, it is disallowed. Your account may have gotten reset.