Or the object(s) could be in a schema that is not the default schema, since the q is written as:
DROP TABLE table1
rather than
DROP TABLE schema_name.table1
Almost certainly not the answer the asker is looking for, but technically valid all the same.
There are a lot of possible reasons objects wouldn't drop.
SQL DBA,SQL Server MVP(07, 08, 09) A socialist is someone who will give you the shirt off *someone else's* back.