Wikimedia Bugzilla is closed!

Deleting an image fails when the filesize is larger than 32767
bytes.

mediawiki attempts to store the size of deleted files in the
fs_size column of table filearchive. The fa_size attribute is
specified as a smallint type, stored in two bytes.

Using a postgres backend, at least, attempts to delete files
larger than 32767 bytes fail with a database exception. 

Executing the following query in the wiki database solves the
problem:

ALTER TABLE filearchive ALTER COLUMN fa_size TYPE integer;