Hi Alla,
This error you have reported is new to 5.6 SP2010 as there was slight change in the way the Microsoft XML parser parse the form component behavior XML configuration. So any XML configuration involving an AND/OR condition that was working before will be broken after upgrading to 5.6.
We already have a 5.6 SP2010 hotfix ready that addresses this issue. Please contact customer support to open a support case and we will be able to provide you a hotfix for this.
Thanks,
Yuan