My servers are all 3.0.25 and configured security = domain. For most users connecting with 3.0.25 smbclient fails. I've compiled and tested 3.0.25a, letting it be the server and trying to connect to it with 3.0.25a's smbclient. The exact same problem exists. I can always connect fine if I just use 3.0.24's smbclient. In fact that is my work around, I've just swapped 3.0.25's smbclient with 3.0.24's.
I have determined the difference between the users I can successfully connect with smbclient and the users I can't connect with smbclient.. If the user's password is 8 characters or less smbclient connects fine, if the user's password is greater than 8 characters then 3.0.25's smbclient will not connect.