I think I have asked this about a year ago, but if you forgive old fart, I need to ask again.
I think the "problem " was that some zipped files are of different format or get unzipped to "wrong" directory or something like that.
I have added zipped library ( DateTime), it shows up in the library list under grayed out "Contributed" , but when I try to add it to my sketch using Import Library it adds a blank line to the sketch.
I did same with zipped Time library and that one adds no problem.
Neither one of these libraries are in "standard" Arduino subdirectory Libraries.
Thanks Vaclav
Addendum
The real issue is - even when I copy the library to subdirectory of all of the other libraries the compilerr still cannot find it untill I give the compiler full path to the library.
The add-on question - where does the "contributed" menu come from and why the compiler cannot link to its libraries.
I think there is an ini file which has the answer. XP is currently searching for it.