You have 2 tasks in progress now.

Did you upgrade from Vista to Win7?

From the error messages there were file transfer problems. For example, when trying to transfer the F747-TONI_KKAL2-11-F747-TONI_KKAL2-10-100-RND3505_3 file from the server to your system the MD5 check failed error was generated. This basically means the file failed the MD5 integrity check and the download was rejected.

I don't know what caused these errors but my guess is it's client side; the tasks that failed to download to your system managed to download to other systems and some have been returned. It's likely that a system restart fixed the problem; resetting TCP/IP settings.

If the systems are all on the same network it might be the case that you need to restart the router. Turn it off, leave it off for 90sec or more, then turn it on and restart the systems. If you have other devices such as a switch, turn them off and on as well.

If that does not work test your general Internet activity is normal.

Perhaps also test your RAM (memtest86 or similar). Faulty chip used as a buffer may be corrupting data in-memory.

Most data corruptions occur during downloads, rather than at Incryption or unzipping (CRC). No other user reports of download problems here would suggest it was a networking issue, this time.

I'm aware that some ISP's are content sniffing and targeting some download file types (including Zip files). Roughly 2weeks to 1week ago this was being tested in a big way in the UK, but it's a worldwide problem. The ISP's are basically targeting online gamers (P2P) and downloaders and imposing download restrictions because many ISP's are heavily oversubscribed.

This system belonging to Ross is showing 8 tasks in progress online, but would only have 4 in reality.

I expect the server remembers sending them, but the client rejected four and didn't tell the server.

Resetting the router did the trick WRT getting new tasks, without network errors.

Data was probably being sent over several different routes, some long, and packet losses kept occurring over the long hops/bad routes. Once the router was reset it picked up fresh DNS information with better routes. Many ISP's change DNS info quite often, but this require new IP info to be sent out, otherwise the client router will be using the same info it has until it expires (days).

The next problem was as you say the ghost tasks, a Boinc issue. In 5 days they should go away - timeout.

Off topic and on your assertion that ISPs should emphatically *never* be interfering with HTTP traffic - ISP's that use silent proxies port filter HTTP traffic (port 80), and many use deep packet sniffing in either so-called tests (40% of all users for years), or on all but the most expensive service. WCG uses 443 (HTTPS), but that doesn't mean ISP's cant restrict traffic in ways that interfere with this download/upload method. Some ISP's don't even know what traffic shaping/management they have in place at any given time. What is clear is that it results in widespread packet loss which nobbles uploads and downloads of all types. Bandwidth can be lowered, contention increased and routing over less favorable connections is also used. Sorry but you can't find such info in a single web page, and restrictions vary with different providers.

http://www.ispreview.co.uk/articles/10_Uncovering_ISP_Fair_Usage_Policies/01.php
http://www.pcpro.co.uk/news/broadband/365782/virgin-upstream-throttling-angers-gamers
http://virgin.net/allyours/faqs/trafficManagementFAQ.html
http://shop.virginmedia.com/help/traffic-management/traffic-management-trial.html
http://en.wikipedia.org/wiki/Virgin_Media
You can look up the other ISP's yourself.