Hi Tim,

Been through all this.  I do agree with you that it's authentication related.  We get the same error when using the same account that the package was built with though.  Note, package is built with BIML but I doubt this is related.
I've ran out of time so I had to re-write using a different HTTP object from .Net.  Problems go away with WebClient.

Seems the .Net objects are more powerful than SSIS ones.  Good of Microsoft to let us reference .Net in the VSTA. 
To be fair many of the examples using HTTPConnection seem to not use authentication.  Now I know why 🙂
Thanks.