• I recently had this problem on SQL Server 2005 SP2 and SP3, and in my case the reason was that there were two identical indexes on a table:

    -1st was a clustered unique index with column1, column2

    -2nd was an index for primary key constraint also with column1, column2

    The server raised the error about foreign key reference when I tried to Drop the 1st index. So the only way I found to trick it was to delete foreign key references and then recreate them...