Error when adding delegate to iExpense Access Authorizations

A user is trying to add a delegate from the iExpense screen Access Authorizations, on 12.1.3.  They are receiving an error:

"The individual you selected does not have expense reporting access for your organization. Please contact your system administrator."  This occurs no matter who they try to add.  But this error does not make sense, because we only have one operating unit.

I have checked user accounts, responsibilities, default expense accounts.  Everything seems to be normal.  The only documents I can find related to this say the error occurs because of trying to add someone from another OU, so they don't apply to us.