Excel Services connection error using SharePoint 2010 to query Analysis Services (2008 RT)

Question

I am connecting to an Analysis Services cube from an Excel Services spreadsheet. SharePoint and SQL Server are configured on separate servers. Am using Excel 2010 / SharePoint 2010 / SQL Server 2008 R2 (RTM) - 10.50.1600.1 (X64).

Refreshing all connections (or clicking an item in the slicer) throws an error: "An error occurred during an attempt to establish a connection to the external data source. The following connections failed to refresh: Adventure Works Cube1"

This from the SharePoint logs: "Refresh failed for 'Adventure Works Cube1' in the workbook 'http://spsatl03t/team/Excel Documents/ExcelServices.xlsx'. [Session: 1.V21.8D/M51Qif9Y+JASEqZsk390.5.en-US5.en-US73.+0300#0000-11-00-01T02:00:00:0000#+0000#0000-03-00-02T02:00:00:0000#-006036.c306da43-6452-40db-9249-6d1e343c79511.N User: 0#.w|kc\svcdms]"

I have configured the below SPNs for my SharePoint and db servers. All SharePoint services run under a single acct (SVCDMS). The SQL Server/ SSAS services both run as SQLService.

setspn -S http/spsatl03t KC\SVCDMS
setspn -S http/spsatl03t.kilpatrickstockton.ks KC\SVCDMS
setspn -S MSOLAPSvc/ddevatl01 KC\SQLService
setspn -S MSOLAPSvc/ddevatl01.kilpatrickstockton.ks KC\SQLService
setspn -S MSOLAPSvc.3/ddevatl01 KC\SQLService
setspn -S MSOLAPSvc.3/ddevatl01.kilpatrickstockton.ks KC\SQLService
setspn -S MSSQLSVC/ddevatl01 KC\SQLService
setspn -S MSSQLSVC/ddevatl01.kilpatrickstockton.ks KC\SQLService

Also, I have NO issues connecting to the AdventureWorks OLTP database via Excel Services. It's only when connecting to an SSAS cube that I get the error. And Kerberos seems to be working just fine. Verifiable w/ this query:

Select
    s.session_id,
    s.login_name,
    s.host_name,
    c.auth_scheme
from
sys.dm_exec_connections c
inner join
sys.dm_exec_sessions s
on c.session_id = s.session_id
order by host_name, login_name, auth_scheme

Interestingly, I noticed here that this was an issue with the beta release, but I'm using RTM: http://social.msdn.microsoft.com/Forums/en-US/sharepoint2010general/thread/46921dd5-4bf8-4ac1-a6d3-13ac4be8cf25

So now I'm stuck. Any help is very much appreciated.