Hi Kamal,
I took a look on this topic, and look on help Data Types - SAP HANA SQL and System Views Reference - SAP Library (table 9) which points that you can convert to varbinary, but not from.
Here I did a quick test and it worked, with a RAW on DDIC ABAP length 16 and the NVARCHAR with length 32.
Check if is possible to you use to_varbinary on attribute from BW DSO source. If not work post some pictures from both sources that you are trying to join.
Regards, Fernando Da Rós
