fragmentation not successful

Why is my code below not working? The fragmentation itself not successful and thus reassembly not working. Please suggest!

switch (stype) {
case 0x00: // Continuation of Message
    msg_seqid = 2;
    rem_length = bctsdu_length;
    proto_tree_add_text(FT_BCnPDU_tree, next_tvb, offset_payload, rem_length, "PDU data : %d", rem_length);
    break;
case 0x01: // Beginning of Message
    msg_seqid = 1;
    proto_tree_add_text(BCnPDU_bom_tree, next_tvb, offset_payload, 2, "PDU Length : 0x%02x (%d)", pdu_len, pdu_len);
    rem_length = tvb_length_remaining(next_tvb, offset_payload);
    rem_length -= 2;
    proto_tree_add_text(BCnPDU_bom_tree, next_tvb, offset_payload, rem_length, "PDU data  : %d ", rem_length);
break;

case 0x02: // End of Message
msg_seqid = 3;
bctsdu_length += 2;
more_frags = FALSE;
rem_length = bctsdu_length;
rem_length -= 2;
proto_tree_add_text(FT_BCnPDU_tree, next_tvb, offset_payload, rem_length, "PDU data : %d", rem_length);
disable_CRC = 1;
break;
case 0x04: // Single Segment Message
—- // doesn't need fragment/reassembly
break;
}
if (msg_seqid == 1 || msg_seqid == 2 || msg_seqid == 3) {
save_fragmented = pinfo->fragmented;
pinfo->fragmented = TRUE;
frag_msg = fragment_add_seq_check(&mns_reassembly_table,
next_tvb,
offset_payload,
pinfo,
mns_seqnum,
NULL,
mns_seqid,
rem_length,
more_frags);
if (frag_msg) {
col_append_fstr(pinfo->cinfo, COL_INFO, " mns segment of a FRAGMENT PDU");
} else {
col_append_fstr(pinfo->cinfo, COL_INFO, " FRAGMENT NOT DONE ");
}
}
if (more_frags == FALSE) {
save_fragmented = pinfo->fragmented;
pinfo->fragmented = FALSE;
rass_tvb = process_reassembled_data(next_tvb,
                                    offset_payload,
                                    pinfo,
                                    "Reassembled Message",
                                    frag_msg,
                                    &mns_frag_items,
                                    NULL,
                                    FT_BCnPDU_tree);
if (rass_tvb) {
    col_append_str(pinfo->cinfo, COL_INFO, "(Message reassembled ) ");
    ALSIGPDU(rass_tvb, pinfo, FT_BCnPDU_tree);
}

}

I am always getting the FRAGMENT NOT DONE error.