Aaaand it’s a BUG! With a fix due in BI4.1 SP5 patch 11 …
SAP has finally admitted there is an issue with my show-stopper problem sending data out of an XML connection in SAP Business Objects Dashboards.
SAP KBA 2244666 - SAP Business Objects Dashboards XML data connection encode error.
I was beginning to think it was just me. But then it probably is just me who uses dashboards in this way!
Debbie
Debbie 
(BOB member since 2005-03-01)
Oh c’mon don’t I get some credit for trying fruitlessly to make it work?
Edit: Also, that number there? 2244666? Maybe there was something to my idea of trying to summon Debbie with pentagrams and incense? 
dstone91 (BOB member since 2015-10-29)
Oh well spotted! ROFL! 
Debbie
Debbie (BOB member since 2005-03-01)
Just thought I’d report that the patch provided by SAP actually seems to fix the problem - and believe me, nobody was more surprised than me at this one! 
Patched my client installation of SAP Business Objects Dashboards, and the test file I’d created to demo the problem now works perfectly.
I will convert all my old dashboards next year, but I am cautiously optimistic …
Debbie
Debbie (BOB member since 2005-03-01)
That’s great news! And, yes, very surprising. 8)
Lugh (BOB member since 2009-07-16)
Update for anyone still awake. Patched my client installation of SAP Business Objects Dashboards. Opened my old Xcelsius 2008 files in the new software and saved/converted everything. No connectivity issues at all! 
That’s Xcelsius 2008 finally ditched, I think. So I’m only a few years behind the frontline now …
Debbie
ETA: One or two tiny issues with resizing the canvas - everything’s a couple of pixels out, but no huge problems. And PREVIEW is a bit flaky …
Debbie (BOB member since 2005-03-01)
I’ve stopped using preview. It takes a godawful amount of time, and often isn’t an actually reliable preview of the behavior of the final product. So I just export it to a SWF file each time I want to view it. Shockingly, this is consistently at least 50% faster than using preview.
Lugh (BOB member since 2009-07-16)
Not to mention, clicking preview causes my version of Excelsius to crash at least half the time
dstone91 (BOB member since 2015-10-29)