Material master classification uploading by LSMW (RCCLBI03)

Hi,

I'm uploading classification for materials, at the end of the process I'm getting the message:

Maintain Classification Data

Error Changing Classification Data

Class Error

( CLAP_DDB_UPDATE_CLASSIFICATION: exception     24  )

The exception 24 refer to this error:  mtart_not_exist

but is not true, my material has a mtart in MARA that exists.

I cannot understand what kind of error is.

Thanks

Best Regards