portable charger


My express switches itself off when I connect it to my portable charger.  The charger is a powermonkey explorer.  The express switches itself off as soon as its connected to the charger and then wont switch back on again until the usb has been unplugged.  I really like my solar charger - does anyone have any suggestions about getting the express to charge from it?  It already has a micro-sd card and the latest firmware.