I don't normally use KDE but I tried installing Kubuntu Hardy on my test machine and each time I close Dolphin I get this message in the attachment below.
It says the error message will only appear once, but it does in fact appear each time I close Dolphin and always (i.e. on every boot). I have plenty of space left on that partition (you can see in the screenshot). I am logged in as the only account on there (the default one) so don't know if it's a permissions thing.
I installed Dolphin using sudo apt-get install dolphin, which might have been unnecessary but the fact still remains that I did! I wasn't sure what the default file manager was and was getting to grips with the KDE interface and the whole Konqueror-is-your-file-and-web-browser thing.
By the way, and this isn't really connected to the first problem, so apologies, is there any way to turn off the single click to open files? I find it quite annoying and don't know how to select a file without having to right click and then cancel the menu that appears. Can't find anything in the settings menu.