This might help others,
Just found out today why /nand/ was full - I found this file .thumbdata3-125478999 in /nand/DCIM
It looks like a thumbnail file, but it was 1.21GB (yes GB) - So I copied it to the PC (just in case I do need it later, but I doubt it) and deleted it from the Scroll, now I have 1.21GB space freed on the scroll, space that is much needed for more useful items.
You may have a large file like this on your Scroll but I guess the numbers will be different to mine, but the file does a similar thing as mine, but is unique to your Scroll.
Anyone know what App, etc. created this file?