Since a few weeks i got trouble to get into the chat in umd.net.

I get a login link but im unable to login.
I have no trouble to login in the main site.

To use the 'chat' thingy you need to check the 'private chat' option in your 'preferences' section of your profile.

If you're having trouble getting the private chat thingy to work for you on a phone or tablet, theres an option to 'show private chatbar on mobile device' in the 'display prefs' bit of your 'preferences' section... Try that!