TransactionScope and Error: ORA-02049

Question

I have the following routine:

For j = 1 To NumItems
    dbValueLookup.Load(j)
 Using scope As New TransactionScope()
        For i = firstIndex To lastIndex

   'dbValueLookup is basically just a Dictionary of items already in the DB
            If dbValueLookup.ContainsKey(i) Then
    'updateData is a subroutine that updates this row with new data
    updateData(j,i)
    rowsUpdated = rowsUpdated + 1
                dbValueLookup.Remove(i)
            Else
    'updateData is a subroutine that adds a new row to DB
                addData(j,i)
                rowsAdded = rowsAdded + 1
            End If
        Next

  If dbValueLookup.Count = 0 Then
            'This commits the transaction - records will be updated when End Using is reached
            scope.Complete()
            If rowsAdded + rowsUpdated > 0 Then
                ShowMessage("Records Updated: " + rowsUpdated.ToString() + " Records Added: " + rowsAdded.ToString())
            End If

        Else
            'We are left with data from the database that was not updated.  This is a problem, so we don't "Complete" the scope.
            'This will result in a rollback.
            ShowWarningMessage("Incomplete Data for " + i.ToString())
        End If
 End Using
Next

Running this against both our production and test Oracle 11g database sporadically (or if there is a pattern, I haven't found it yet) generates the Oracle Error: ORA-02049: timeout: distributed transaction waiting for lock

Since this is the only process running against the test database, there shouldn't be any issue with different users competing for a lock.

Any ideas what might be causing this error?

Thanks in advance.