Process Builder Error Message - Flow Failed to Access Value for my Variable....

Hello,

I am trying to create a process builder flow to update all Child Accounts when the Parent Account field "X" is populated, then update all child account field "X" = Parent Account field "X".

I am getting an error message that say "The flow failed to access the value for myVariable_current.Parent.SW_License_Activation_Date__c because it hasn't been set or assigned.."

Criteria runs when parent field "X" contains is null = False, then

Update all child account field "X" fiedl reference [Account].Parent.X

Any ideas why this is failing?

Thank you in advance.

Kim