Could not Create Full TEXT INDEX- SUM ERROR- MAIN_POSTPROC/JOB_RSFIXUPG

Solution: 

From SE14 ,

Check the indexes that exists for that table.

Usually SAP SUM will try to create a new FULL TEXT INDEX with a different name as a standard and as there are already indexes available, it fails to create the new INDEX with the error "SAP DBTech JDBC: [289]: cannot use duplicate index name:"

From SE11, 

Drop the existing FULL TEXT INDEXES and re-run the SUM STEP

Commands that are helpful : 

DROP FULLTEXT INDEX "<table>~<index>" ON "<Schemaname>"."<table>" 

CREATE FULLTEXT INDEX "<table>~<index>" ON "<Schemaname>"."<table>" ("TXT20") ASYNC LANGUAGE DETECTION ('EN', 'DE') PHRASE INDEX RATIO 0.200000 FUZZY SEARCH INDEX ON SEARCH ONLY ON FAST PREPROCESS OFF TEXT MINING OFF TEXT ANALYSIS OFF TOKEN SEPARATORS '\;,.:-_()[]<>!?*@+{}="&#$/' COMPRESSION LEVEL 0