I had a similar problem recently. I have a linked excel file but I need to append it to another table each time the excel file is updated. But the append would not work.
In the query I appended this instead
cstr(nz([MyExcelFileName].[MyColumnName],"")
The meant that whether I had numbers, text, or blank in my input record, Access always appended TEXT to the destination table.
Does that help you?