It has to do with the ROM size allotment ("partitions" for lack of a better anology) that the BL determines. Here's a post and gguruusa notes the sizes:
http://forum.ppcgeeks.com/showthread.php?t=33459.
The ROM has to fit in the space provided or you get pre-boot problems, stuck at bootloader or splash screen. So you have to be careful when cooking your ROM in the kitchen or loading pre-made ROMs as they are frequently not advertised per compatible BL (Helmi's were though). The BL 1.00 should have no problems as it is the biggest. Idk why you were able to flash the WM6 ROM the second time but not the first time with the BL 2.02. I doubt if the store would take the time to figure out the BL problem. I would have just taken it back and I think after three times they give you a 6800!
