i have been using it from 10th august and has not yet recieved any credit ....there is always a client error ...What is it can anyone explain it...i m using windows 2000 and service pack 4

If the one you are currently running doesn't last very long, try a project reset (from the projects tab). A file could have gotten corrupted in the download and needs to be downloaded again.

You've had 16 results where the initial download has failed. It looks like you have managed to download successfully now, but if your current model also fails it might be worth downloading the <a href="http://arnaudboinc.free.fr/slab413/slab413.zip">zipped up applications</a> that Arnaud has made available for anyone who's having download problems. All you have to do is unzip the files to your projects/climateprediction.net directory before you start running BOINC.
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thanks ..It's working now