Horde login problem

Running WHM 11.2.0 cPanel 11.10.0

Noticing a random problem with logging into e-mail using Horde.

1. We go to www.domainname.com/webmail
2. Login box pops up and we provide username/password
3. The cPanel screen appears with the standard options (Change Password, Autoresponder, etc.)
4. We select the only webmail client we have active..."Read Mail using Horde"
5. The language selection screen comes up properly and we select "login"

This is where the problem occurs. It grinds for a moment or so then gives an error of:

"Login failed because your username or password was entered incorrectly."

The page then redirects to a blank page.

This same thing occurs if you try to login to the account through the cPanel Mail section for the particular site.

There are other domains on this server where the Horde login works fine, using the same procedure as above, but others are failing the login. We can't find any common thread for those that work and those that don't. It appears totally random.

Anybody else run into this and have a fix?