I'm not too sure about what version it changed in, but in newer versions the number of params to selectall_hashref has changed:
This utility method combines the prepare, execute, and fetchall_hashref entries elsewhere in this document into a single call. It returns a reference to a hash containing one entry for each row. The key for each row entry is specified by $key_field. The value is a reference to a hash returned by "fetchrow_hashref".