This statement tries to create an index with the name shown, but an index of that name already exists. Only one index of a given name can exist in a single database.
Check the spelling of the name. If it is as you intended, and you are sure it should not exist, make sure you are using the right database. To review the names of all indexes and their owners, join systables and sysindexes as follows:
SELECT T.tabname, I.idxname, I.owner FROM systables T, sysindexes I WHERE I.tabid = T.tabid AND T.tabid > 99