Actually we have same problem. My Kcvds is always says like that when i try to connect. Its doesnt matter, i think its because my connection is so slow and its caused me so hard to connect the server, but its not a mistake if u Try this :
enter your username and password as usual, BUT, after that, u click Yes Repeatly until 3 or 4 times, the messege pop (database error) will appear by multiple but You can login sucessfully after that.. Iam always do like this if i want to play in Kcvds and it succeed, i hope. :D