The first thing I do when I have an error I can't work out, is paste the important part of the error into the forum search box. 9 times out of ten, it's happened before.
The important error in your output is the fatal one right at the end (SS will still work with Notices). So I search for "Class 'Extension' not found" in the forum and got this post from a while back from someone with the exact same issue. (I looked because I knew I had seen this before)
It seems that some archivers may do something bogus to the archive when it is unpacked. (I for one never knew ACDSee had an archiver)
I would download the trial of winrar [url]http://www.rarlab.com/download.htm[/url] (first link at the top) and try unpack a fresh copy of the archive.
Post back here with the outcome, because the original poster in the above thread failed to do so, although someone else replicated the problem and found it was solved after using winrar.