In LTRC, Loaded table turned out to be "tablename_1"

I used LTRC to load some tables, some of them failed. I can't clean up the failed table from the table overview. Maybe because I reload the tables again, there  were some load table named previous tablename plus "_1".

Two questions:

1. How these "_1" tables appeared and how to solve them?

2. How to clean up the failed tables to restart the whole load process?

Thanks a lot!