error 12115 and how to delete a smart blob

hi during dbexport of my db, i have got an error ---- *** Error fetching data row. 9810 - Smart-large-object error. 12115 - Smart Large Objects: The LO header page is a wrong length - probably corrupted. --- Using finderr, i found: ------- An internal error probably occurred and corrupted the LO header. Delete and recreate the smart large object or restore the sbspace from an archive. --------- Then, i found the line of my table where the corrupted blob is (the first not in the unload file) and try to remove it. delete from document where id_document=nnn fail, same error. update document set name_of_sblob_column = null where id_document=nnn fail, same error. drop and recreate table... fail, same error. So... how to remove the line or the blob, and continue my export ? thanks DKano