You receive credits for those invalid results because they returned error free, as you said, with return code 0.

Many crunchers would simply take the credits and not worry that a 4th WU needs to be sent out. Glad to see you're taking the time to fix the problem, WCG needs more dedicated crunchers like you

Take a good look at the suggestions Sekerob offeres, run the diagnostics, etc. Yes, overclocking will sometimes cause the problem you are seeing, other times overclocking causes no problems.

If Sekerob's suggestions turn up nothing then (and only then) consider the following... Another possibility is that the result files get corrupted when you upload them. The "report and upload" process is a 2 stage affair. First your system uploads the result. Later, your system uploads the report. The report is a much smaller file and it tells the server whether Autodock exited with 0 or an error. Small files like the report are less likely to get corrupted during upload, large files like the result have greater chance for corruption.

U did not answer the BOINC version query..... what Dagorath is pointing at is, i think , the possibility of antivir / firewall or other security software doing odd things.....unpacking / repacking then letting thru can do odd things too...put a bit the wrong way and u have no match.

BOINC had an issue with McAfee (latter doing something none-standard), so Berkeley released a new version....the recommend version by WCG is actually 5.4.11

Well, as mentioned in my first post: I'm using BOINC Client Version 5.6.1 in the meantime. CC stands for Core Client which is the same as the BOINC Client.

How to check if the Firewall is the source of the problems ? I'm using CyberArmor Personal Firewall.

No, that is not what I was pointing at. I was suggesting maybe the phoneline, DSL cable, ethernet cable or some other copper between him and his ISP is bad. He replied saying he has ruled that possibility out becaue he has used 3 different connections. That's a decent test of my theory/suggestion but I wonder if he has used the same cable to connect his computer to the modem in all 3 cases. If it's an internal dialup modem then it could be flaky too.

I doubt a firewall or anti-virus would corrupt the files. A firewall would simply not let the file upload. Anti-virus would decompress to inspect the file but would not waste time recompressing, it would just send the original file, unless it's really stupid anti-virusware which is possible but I doubt it. Anyway, I doubt he's using compressed uploads, compression is not allowed yet, AFAIK.