I remember years ago some kind of issues when which finished the migration from exchange 5.5 to exchange 2003 and from NT 4 to Windows server 2003. The problems arise cause the connector between the two domains failed and exchange server 5.5 never was remove as should have been.
After that we rise the domain, the forest level and exchange to native mode.
Now I'm having an issue when trying to add a distribution list as contributor to a public folder.
The exact error is this Event ID 9556
Unable to set permission for DL /o=OLD INSTITUTION NAME/ou=NEW INSTITUTION NAME/cn=Recipients/cn=DASNT because it could not be converted to a security group. This most likely is because your system is in a mixed domain.
I also get the warning Event ID 1233
An error occurred.
Function name or description of problem: EcCvtDLToSecGrp
So, what can I do to force the native mode. Right Now exchange said that is already on Native mode