Error Msg

[S. R.]

I'm trying to do inserts into my database and I'm getting the error :  "duplicate entry
'2024' for key 2"

I'm guessing that
2024 is my primary key (ID)
and key 2 would be the column title in my table.  when I do a desc it says  "MUL" under
key.

Can someone explain what MUL stands for?  Does this error mean that there is another entry
in the table with the same title?  I did a search on the online manual for references to
"MUL" and read the sections on foreign keys but found nothing with "MUL".

TIA