This won't fix anything but it will make your code run faster. The guard time around the +++ is 1000ms by default. So I usually only delay for 1010ms (an extra 10 just to be safe) before moving on. This works fine.
Also, check some of my pretty old sample code for a kinda dumb but easy to read function for checking the OK in command mode: http://www.faludi.com/itp_coursework/meshnetworking/XBee/XBee_Send_Example.pde