teamcity nuget server doesn't serve package to build process

I have a class library project ('D') built in TC with MSBuild.  The next step builds a package and puts it in the TC nuget server.

After setting up the right feed source in visual studio, i can see package D after being built by TC.

I have another project ('R) that consumes the above package.  I have added the package to the 'R' project in visual studio, and it compiles without errors.

In TC, the first step to building 'R' is to restore packages.  However, when 'R' is built, it fails with an error: 'Unable to find version 'XXXXX' of package 'D'

Going back a step in the build log, the NuGet package restore step complains about the access to the feed svc url as 'Unauthorized'.

But how do you enter credentials for the internal nuget server?  

Oh yes, this happens with both the authorized and guest url.

thanks in advance

david