We still may want to implement a bulletproof check for the current version, and a better place to add this message so that it works for all kind of other errors too.
If the test was run before the YoutubeIE tests (for example by running
"nosetests -v test/test_compat.py test/test_download.py -m 'Youtube_1|compat_expand'"),
it wrote the signatures cache to the 'C:\Documents and Settings\тест\Application Data' folder.
It failed due to a problem in the cache code and the write_json_file function (fixed in f03e33b89a622af13fa5275c46b63aaa4814c499)