The problem occurs because you can't really uppercase a ß character because there is no uppercase equivalent.
On Windows, if you convert "ß" to upper case, nothing changes, you get left with "ß".
On a Linux/Java setup "ß" gets uppercased to "SS" because that's what the Unicode spec says.
This leaves a major incompatibility for German users where JCIFS can't connect to a Windows CIFS share with a "ß" in the folder name.
A similar issue also exists if a username contains a "ß" character. In this case the authentication fails because the hash isn't correct.
I know someone is probably going to say this is not a JCIFS issue, but there really needs to be an interoperability fix in JCIFS so that it can work well with Windows shares for German users.
I was think along the lines of subclassing java.lang.String and introducing a workaround into the toUpperCase() method.
Here is some previous discussion on the topic for background reading:
3. And a similar fix from JLAN https://issues.alfresco.com/jira/browse/MNT-1409