When there is an inbound IDoc process for ASN program there are some modules that are called. /SPE/CL_IBDLV_CONTROL makes a call for module CONVERSION_EXIT_ALPHA_INPUT. This happens because of the parameters an here length is considered. Is_drm1-partner_id that has the character length of 17 and Is_vbpa-lifnr is 10 in length. This is one part and the other is related to the input field and according to this if there are 10 characters in the field then system gets dumped with an error. Generally, the error that is noticed is CONV_EXIT_FIELD_TOO_SHORT and it is noticed each time when the user provides this input.