I have a dataflow that connects to a SharePoint site to fetch all Excel files (there are several hundred) and combine them.

When I do a scheduled refresh, it takes about 18 minutes to refresh successfully. However, when I turn on incremental refresh, after about an hour it fails saying:

DataSource Error: SharePoint: Request Failed: The remote server returned an error (429) (429 TOO MANY REQUESTS) 

Why is this happening and how can I resolve it?

I’ve read about Odata feeds, but this doesn’t work when trying to retrieve data from files.

Please don’t mention databases, I know that’s the right way to do things but I don’t own the company and can’t change the fact that they use Excel files.