You may face this problem after upgrading from Exchange 2007 to Exchange 2010.
During Implementation of Exchange 2010 the old transport rules will be copied from Exchange 2007 to Exchange 2010 new location (the format and location of the transport rules are changed in 2010).
However you may have the disclaimer is working fine from users in Exchange 2007 (because they are using HUB 2007) and not working for the users in Exchange 2010.
The problem here that disclaimer in condition “Outside the organization” will not work when not having out of the office and legacy messages allowed to external, the solution is very simple as the following snapshot:
Restart the transport service on all hub servers you have and the disclaimer will be applied.