I just downloaded both the With and Without sources packages for NET4.0 Professional Studio .NETHTML5 Beta3 and unzipped them with 7Zip and there was no problem.
To make it absolutely certain that we are talking about the exact same links, I used the following links:
Also, to make it absolutely certain that I am focusing on the correct problem, then it was my understanding that after the download, you tried to unzip it via 7Zip and then you got an error, correct ?
The most likely cause of your problem is a badly cached copy of these files somewhere between you and the storage provider where we store the uploads. This could be on your own machine, this could be on a proxy you use to access the internet or this could be on some other caching medium at your ISP or some medium between you and the host. You can rule out your own machine by trying to download on another machine. If you are able to download without going through the proxy, you can rule out the proxy etc.
If all fails, I may be able to upload a special copy of the exact file you need to download, so you can try again using a different path.