Hi Hope -
I use Oracle a lot and have seen this happen with more than just Oracle.
When this happens I close out and go back in and it works.
If this happens every time you try I'd suggest opening a support ticket.
Hope it is working now!
Thanks for the feedback. I think perhaps this query was just too complex for the custom SQL. I've tried breaking it into smaller pieces and am getting a preview back.
Now on to figure out other issues:).