uploading base unit of measure BAPI_MATERIAL_SAVEDATA thru LSMW

I'm uploading the material master thru LSMW using the BAPI BAPI_MATERIAL_SAVEDATA (BUS1001006) and I'm facing the following problem:

The input data is provided in the tab delimited file .

While uploading if the sales unit is left blank in the input file (when Base unit of measure = sales unit) I'm getting the error " The value is not allowed for the field NARM-MEINH/BAPI_MARM-ALT_UNIT".

As per requirement in the input file if the base unit of measure and sales unit are same then sales unit field is left blank.

In my case diff values /same values are provided in the input file it is working fine .

Please help its required urgently.