“​Why would I get the message ‘There is another user already merging records. Please try again later.'”

This message will appear if there is another user using MergerSeries or the system crashed while using MergerSeries.  If there is no other user, you can clear any existing users from the activity file.  If on SQL Server, you can delete the records from the CRG_ACT table, otherwise, delete the CRG_Activity table from the Sales folder.