Using Branch With XPO

I get the following error when I try to save a Branch Security System User - LARRY-PC\Larry

Xafari.BC.Branches.Xpo.BranchSecuritySystemUser.AvailableBranches is not a collection property. It should be labeled with AssociationAttribute and be of the XPBaseCollection descendant type. Probably, you use GetCollection in the situation where GetList should be used.

I really need to use Branch in my current XPO based application. Could you let me know how I can implement the suggestion in the error message?

Thanks,

Larry