If you use Active Directory authentication and are using Open-AudIT 1.12 it will likely be failing.
You can confirm this by setting the log_level to 7 in Community (menu -> Admin -> Config), logging out and then attempting to log in to Enterprise using an Active Directory account.
Check the log file at (Linux) /usr/local/open-audit/other/log_system.log or (Windows) c:\xampplite\open-audit\other\log_system.log and you will likely see entries as below.
Mar 07 15:42:39 YOURSERVER 2060 5 U:Open-AudIT Enterprise C:main F:get_count I:127.0.0.1 M:open-audit_enterprise Active Directory failed verification (html request)
To fix this issue (before we release 1.12.2) you can edit the file:
Linux - /usr/local/open-audit/code_igniter/application/models/m_userlogin.php
Windows - c:\xampplite\open-audit\code_igniter\application\models\m_userlogin.php
You need to remove the clean_sql function, so please replace line 47 with the below.
$sql = '/* M_userlogin::validate_user */ ' . $sql;
And please replace line 126 with the below.
$sql = '/* M_userlogin::get_user_details */ ' . $sql;
This bug has already been fixed for our next release. Apologies for any inconvenience caused.