Ok guys. I sorted my problem out. Thank you Fluid.
I am on 4.0e, cios 38 rev 12 (wani's) and usb loader gx revision 576.
Installing a patched ios60 sorted out 4 problems that I was having :
1. I can now close one game, open usb loader gx again and play the next game without having to restart my wii.
2. In can now copy / move saved games and channels from my sd card to wii system menu without getting the "may not have been copied / moved" error.
3. I can launch my wiiware channels from my sd card.
4. After closing one .avi file on mplayer CE, I can immediately access my usb storage and choose another one to play without having to first exit HBC and restart it, which was the case before I installed the patched ios60 .
So, just look for a patched ios60 wad or IOS60-61_Shop_Mii_Installer and bob's you uncle.