mysql upgrade table/mysql check questions

hello
when i make check tables attachments, i get the information

rt3.Attachments | check | error | Table upgrade required. Please do
"REPAIR TABLE `Attachments`" to fix it! |

when i do this, or mysqlcheck --check-upgrade --all-databases --auto-repair
all is fine, he says tables repair but the table is still (after a new
check) not "Upgrade" all other tables are.

Cause of this , i cant dump the database, (he crash, with this failure)
any ideas (?) it is a InnoDB Format.
friendly regards

i forgot to wrote what happens after repair
mysql> REPAIR TABLE Attachments;
+-----------------+--------+----------+-----------------------------+
| Table | Op | Msg_type | Msg_text |
+-----------------+--------+----------+-----------------------------+
| rt3.Attachments | repair | status | Table is already up to date |
+-----------------+--------+----------+-----------------------------+
1 row in set, 1 warning (6 min 30.36 sec)