Sounds fluid based issue to me, or some residue has been dislodged and has messed up a shift solenoid.
Alas, this box has internal solenoids as opposed to an external valve pack, so if this cannot be restored by fluid change (maybe another flush needed sorry to say) and CORRECT level filling then the case has to come apart. Which means box out
http://www.matthewsvolvosite.com/for...38920&p=185380