SQL Server 2012 :: Merge Statement Using SCD2 Failing?

I have created mergse statement using SCD2.where I am inserting the data if my BBxkey is not matching with target and updating the rows if the bbxkey is matching and rowchecksum is different.

Working of Store procedure

There are 2 scenario covered in this procedure on the basis of that ETL happening.

There are 2 columns deriving from source table at run time, one is BBxkey which is nothing but a combination of one or more column or part of column and another column is a Rowchecksum column which is nothing but a Hashvalue of all the column of the tables for a row.

Merge case 1:-WHEN NOT MATCH THEN INSERT

If source BBxkey is not there in Archive table that means if BBxKey is null then those records are new and it will directly inserted into Archive table.

Merge case 2:-WHEN MATCH THEN UPDATE

If Source.BBxkey=Target.BBxkey && Source.Rowchecksum<>Target.Rowchecksum then this means source records are available in Archive table but data has been changed, in this case it will update the old record with latestversion 0 and insert the new record with latestversion 1.

my sp failing when source having more than 1 same bbxkey.

error [Execute SQL Task] Error: Executing the query "EXEC dbo.ETL_STAGE_ARCHIVE ?" failed with the following error: "The MERGE statement attempted to UPDATE or DELETE the same row more than once. This happens when a target row matches more than one source row. A MERGE statement cannot UPDATE/DELETE the same row of the target table multiple times. Refine the ON clause to ensure a target row matches at most one source row, or use the GROUP BY clause to group the source rows.".

Sample store procedure

DECLARE @Merge_Out TABLE (Action_Taken varchar(8),
TimeIn datetime,
BBXKey varchar(100),
RowChecksum nvarchar(4000),Col001 varchar(8000),Col002 varchar(8000),
Col003 varchar(8000),Col004 varchar(8000),Col005 varchar(8000),

[code].....

How Can I avoid such failure of my sp.

I want to handle those case where S.bbxkey=T.bbxkey && s.rowchecksum=t.rowchecksum