change password in owa Exchnage 2010 ,

Hello everybody!

Faced with strange trouble in OWA (Exchange 2010 SP2) - trying to change password for each user - some can change password, some - not. They are receiving message: "The password you entered doesn't meet the minimum security requirements." All the users is in same container (AD), group policy is the same for all... I have 2 DC's, replication has been successfully finished. I tried to run - gpupdate /force on both DC's - also successfully. But some users can change password only using Active Directory - I mean "Reset password". Please advice ?

thanks ,