[Koha] Need help regarding data migration

[Tanzeem M.B]

I am migrating to koha.I got a spreadsheet with the present data.
I have found the marc21 tag info details for each column.
eg. Accession Number 541##$e.
I am using MarcEdit 's Delimited Text Translator.
When I tried to map data and click Add argument, MarcEdit gives the
following "Mapping Error."
" Field / Subfield combinations must be defined at 245$a
  It appears that your intention is to create such a pair.
  If that's the case please click OK and update the mapping. If your data
is not
  a field/subfield pair, click cancel to ignore this, as well as future
messages.
 "
But when I click ok, I get the same message,
And when I click cancel cancel the data is added to the Arguments text area
like :
0 541 ##$e 0
Please help me to proceed further.

​with thanks and regards
Tanzeem