Normally, When we try to DELETE the statistics using the following statement, The Error occrred
DROP STATISTICS TableName.StatisticsName
Msg 3739, Level 11, State 1, Line 1
Cannot DROP the index 'Table.StatisticsName' because it is not a statistics collection.
The reason is, The statistics name we going to DELETE should be a Statistics collection.
What is statistics collection ?
"Creating statistics on multiple column on a table"
How to create ?
CREATE STATISTICS StatisticsName ON TableName(Column1,Column2)
Now the statistics collection can be deleted.