New Post: The HTTP request is unauthorized with client authentication scheme 'Ntlm'. The authentication header received from the server was 'NTLM'

I worked out my issue. I read elsewhere [some other thread on here] that loadbalancers can cause this error. I got an IP for one of the SP WFE's and set an entry on the SSIS server's HOSTS file so the call to the site would go directly to a single WFE. It works!

I did also have to create a configuration file to hold the username & password. But I had already done that. So, for me, it was the IP thing IU mentioned above that was the missing link.

Hope this helps!