As you say, you only removed the rockbox.iaudio file so the rockbox bootloader is still installed and is trying to read that file on boot.
Reflash your x5l with cowons orignal firmware and you'll have a stock x5l again.
Oh, wait. Did you remove the rockbox.iaudio from within rockbox? Hmm... That's not going to help you at all.
Ok, then we HAVE to solve your connection problem;
How do you do when you connect your x5l to your computer? Is it started and running rockbox?
I've got an x5 too, albeit not an x5l and i don't have any issues hooking it up to my computer.
I almost always connect my x5 from turned off (computer turned on) and that means that no rockbox code is ever executed.
It's got two modes when connected via usb like that, either disk mode or 'charge mode' toggled by a long 'press' on power.
Oh, by the way: You are not using the usb-port on the side are you? You have to use the usb-port on the mini-dock.