Loading error query

Hello, I am loading data to standard dso from write optimize but keep getting this error message while activation:

Error while writing master record "???" of characteristic 0MAT_PLANT

and In my transformation 0MAT_PLANT is not mapped to anything. it is not mapped from datasource to write optimize and from write optimize it is not mapped either and there are no routines.

What do you thin kthe problem is?

Thanks.