vBulletin: users can’t login nor change passwords after update [SOLVED]

Since installing the latest security patch releases for vBulletin, some problems arise:
1) members who change their passwords cannot login.
2) new members can’t login after first login (this is, if they logout after activation, and then try to log in again, they can’t)

In both cases the user gets the standard error message (like the one that shows up when entering a wrong username or password).

To solve this issue, you should follow this steps:
- Go into your database (using phpmyadmin, for instance) and look at the user table (vb_user) and more precisely to the field called salt. Lengh should be 30 (AND NOT 3!). If the lenght is not correct, change it to 30. It should end up being like:

- Browse your FTP server, open includes/class_dm_user.php and see at around line 18 if the define for salt is set to 30. It should be like:

define('SALT_LENGTH', 30);

Both those values should be 30!

This affects to VBulletin 3.8.4 and vB4

BIG DISCLAIMER: Backup your database and files before doing any changes…