Make sure that you’ve uploaded wplistcal.php directly into the root of your plugins folder.
It must not be in a subfolder (as with other plugins) – that seems to have sorted it for me anyway (although I’m having another problem with saving my settings…)
The answer is correct, although it’s a pity that the error is there.
If you use the One-Click installer http://anirudhsanjeev.org/projects/oneclick/ with the download link at ww.wp.xz.cn, then it automatically puts in the wplistcal subfolder. I guess that’s because the zip file is a zipped folder rather than a zipped file collection.
Either the files should be zipped without the folder, or the plugin code should assume there is a containing wplistcal folder.
