I am posting this in case someone else has a similar issue using QlikSenseDesktop and they get and unexplained "Connector Reply Error"
I had an existing data load script in the data load editor which was grabbing data from a MS Access database via an odbc connection.
My data source/table was an Access query.
Previously I had manually added new fields to the load editor script without any problems.
After a specific new field I started getting a "Connector Reply Error" * when trying to load data.
I learned that my Query in MS Access had the same field name listed twice (the new field I was trying to add to the script).
It makes sense now that I see it. but the problem was difficult to identify.
Note: If you preview your data with data connections->'select data' the duplicate fields may be identified by field names starting with "expr:".
I hope this helps.