Is the Rockbox bootloader already installed on the device?
That is to say when you power on the device does it attempt to load Rockbox or does it go straight into the sansa firmware?
You say you had it installed once before, I can assume that the bootloader is still installed.
So, I would imagine all you need to do is copy the .rockbox folder to the device.
To simplify this process, remove any unneeded USB devices from your computer. Also remove the MicroSD card from the sansa player.
Connect the player to the computer and attempt to browse to the device.
Obtain its drive letter.
Now start the RB util.
On the top right of the utility, ensure the selected device model matches your device model.
Ensure that "mountpoint" is the same drive letter you just obtained.
If it does not match click "change" and make the necessary adjustments.
Under the "rockbox version to install" choose either the stable version or the development version. You are concerned about the panic aborts. If you had these aborst with the stable version I suggest you try the development version. However, the names would suggest that you'll have the most luck with the stable version

[Once again, I am going to assume that you have the bootloader already installed]
Uncheck "bootloader"
check "rockbox"
check "fonts"
uncheck "themes"
uncheck "games"
click install.
after some time, if it worked, you can test your device.
if all went well you can reconnect the device, uncheck everything and check "themes" if they are desirable.