Seems down (Error 500). However, the books that were published can be viewed at Monoskop: http://monoskop.org/log/?p=10127

For those who are interested in Klee's personal notebooks, this collection of Bauhaus eBooks on the same site could also be of interest (iirc, HN brought me to these a couple of months ago): http://monoskop.org/Bauhaus#Books