Your move issues does sound like it's purely due to sorting. When sorting is on, you have no control over the order other than changing the content of the row that is being sorted on.
As for the error message, could you please contact our Support Humans at
omnioutliner@omnigroup.com so we try to figure out what's going on. Also please include what version are you using, OmniOutliner 1 or 2 for iPad.
Thanks!