We are setting up for a cross forest migration, with Exchange 2010 in the old forest and exchange 2013 in the new Forest. I have setup galsync using FIM 2010 R2 Sp1. I am using the default Management Agents with no modifications. When syncing mail enabled users from the Exchange 2013 forest back as contacts to the Exchange 2010 forest I am getting an error for each account. After every export run of the management agent a duplicate contact is being created. This is holding up the migration and I have not found anything online except this forum post, which does not explain how to resolve the issue in any detail.
This is the error I am getting in the event log, it is an "ma-extension-error"
"The property 'AddressListMembership' is on a read-only object and can't be modified"
Supposedly there is some sort of way to hardcode the exchange version to 2010, instead of 2013, which resolves this issue. I assume it is a hack or workaround, but I am quite perplexed why there is no info from MS about this.
If someone could give me detailed instructions on how to get around this problem I would be most appreciative.