Hi,
Today morning got the same error in BO when i tried to access the bex query but OLAP connection is working fine for me.
So i tried to execute Bex query in bex designer and its ended up with error and i reported to BW team and BW team resolved this issue. Now I am able to use bex query in BO without any issue.
So please execute bex query in bw side and check whether its working fine. Nothing to be done in BO side.