Run time error during invoice creation using BAPI_INCOMINGINVOICE_CREATE

Hello Experts,

While creating GR based Subsequent credit for self billing inovice for Portugal using BAPI_INCOMINGINVOICE_CREATE

i am getting a run time error "Unable to convert 'B' as a number".

Reason is while generating Number range,for ERS process, IVTYP is defaulted with value 'B'.But am not passing

any value to IV_CATEGORY.

I am passing below fields at header lever,

invoice_ind  = space.

comp_code    = gw_bukrs.

doc_date     = sy-datum.

pstng_date   = sy-datum.

ref_doc_no   = invoice number .

currency     = 'EUR'.

item_text    = descr.

and  below fields and item level,

po_number        = f_ekko-ebeln.

po_item          = f_ekbe-ebelp.

ref_doc          = f_ekbe-belnr .

ref_doc_year     = f_ekbe-gjahr.

ref_doc_it       = '0001'.

tax_code         = 'D4'.

quantity         = 1.

de_cre_ind       = gc_x.

item_amount      = 10.

po_unit          = 'PC'.

Does anyone have any idea about the reason for this error.?

Thanks in Advance,

Gowri.