Here's our problem, users who want to change their password trough OWA get this error "The password you entered doesn't meet the minimum security requirements.", even if users are respecting the minimum security requirements.

With these settings, we have the error:

Enforced password history                          1 passwords remembered
Maximum password age                               185 days 
Minimum password age                               1 day
Minimum password length                            7 characters
Password must meet complexity requirements         enabled

With these test settings, we don't have an error:

Enforced password history                          not defined
Maximum password age                               not defined 
Minimum password age                               not defined
Minimum password length                            not defined
Password must meet complexity requirements         not defined

People can change their password but there is no more security!

Just changing one parameter of the GPO for example "Enforced password history", brings back this error.

Here's our server configuration :

Windows Server 2008 R2

Exchange Server 2010 
Version: 14.00.0722.000

If anybody has a clue it would very helpful !