Replica server 8.5.2 - 6.0.1

when I try to schedule a replica from servers I get this error:

Unable to store document in domino/xxx xxx\xxx.nsf (NoteID = 0) from xxx/xxx.nsf (NoteID = 5950466): This function is not implemented on this version of the server

Unable to store document in domino/xxx xxx\xxx.nsf (NoteID = 2058) from xxx/xxx.nsf (NoteID = 2058): This function is not implemented on this version of the server

Unable to replicate domino/xxx xxx\xxx.nsf: This function is not implemented on this version of the server