Welcome to Mobileread!
calibre is updated weekly; is this error new? Which version of calibre?
calibre creator, Kovid Goyal, is extremely responsive in the
calibre forums, as are all the calibre developers! If you haven't already, visiting there would provide some assistance.
calibre itself can be found
here. Along with the addition of the plugin '
Kindle Collections' designed by forum member
meme, the creation of a storage system e.g. collections on kindles is spot on!
