SB5101E canot be flashed over serial, you should buy it this, i used this to flash my sb5101E is so easy just solder pins in board. chose IDC cable 10pins http://www.embeddedcomputers.net/products/FlashcatUSB/
http://www.haxorware.com/forums/showthread.php?tid=3597
http://www.haxorware.com/forums/showthread.php?tid=3300
http://www.haxorware.com/forums/showthread.php?tid=3597
http://www.haxorware.com/forums/showthread.php?tid=3300