From: GK on
I recently knocked my head against the wall trying to figure out how
to paste Excel data into a SharePoint list where one of the fields in
the list was a Choice field (checkbox), with multiple selections
possible. It kept giving an error. I could find no documentation for
this issue anywhere, and would like to share the solution I eventually
discovered.

In Datasheet view, multiple values in such a field may look something
like this:
A;D;F
where A, D and F each represent one of the multiple values in the
field.

If you export the list data to a spreadsheet, the values mentioned
above will display like this:
A;#D;#F

If the spreadsheet is still linked to the list, you can, of course,
simply edit that field using the same approach -- a semi-colon and a
pound sign as a separator between the items. You would expect that the
same format would work for pasting data from
an Excel spreadsheet into the Datasheet view of a list. However, this
is
not the case.

In order to successfully import the values given in the example above,
those values in Excel must be formatted like this:
;#A;#D;#F;#

In other words, a ";#" must appear at the beginning and end of the
selections, in addition to being used as a separator.