See post http://www.worldcommunitygrid.org/forums/wcg/printpost?post=231625

Add HCMD2 and HFCC to the list of confirmed. FAAH also seems to benefit, so with that guess all projects will have a gain of some sort.

Clients, since WCG does not provide 64 bit packages, probably this version http://boinc.berkeley.edu/dl/boinc_6.2.19_windows_x86_64.exe is what you want to go with on Vista. Can't recommend 6.4 at all and 6.6 with reservation.

why not 6.6?

I don't think it is ready for prime time but if you typically do not need much BOINC support and are OK with a bit of scheduler oddities and only crunch WCG you should be fine. I have had not problems processing the actual WUs.

1. Elapsed time is wall clock and not actual cpu time so people quickly become confused and think something is wrong when a WU says it has been working for much longer that typical. For example RICE is 7 hours fixed but if interupt its processing you may end up with many hours of elapsed time over the target of 7 hours long before you reach the actual CPU 7 hour limit.

2. This is related to the first issue in that it seems like it uses wall clock elapsed time in the estimate WU runtime length / scheduler formula. Because I only run WCG does not mean much but it sure looks weird. The example here is that I had some CEP WUs pre-empted for betas a few week ago and when the betas were done (all finished quicker than the estimate) somehow my CEP estimate went from ~6 hours to 8+ hours each. Same thing happens if I stop running WCG (gasp ... heresy ... never stop :-) for a few hours ... individual WU estimate go through the roof. Now it really does not take more than a day or so to get the time estimates accurate again but it points out that the scheduler is screwy.

Your problem is that all 32-bit programs on win64 is installed to "\program files (x86)\" while 64-bit programs is installed to "\program files\"

Since on downgrade you always must uninstall current BOINC-client, v6.4.xx and v6.2.xx will always move the files back from the BOINC data-directory to the program-directory, meaning if you switches between 32-bit and 64-bit the files is located in "wrong" location.

To fix, you'll need to copy from the old "\program files (x86)\" BOINC-directory to your new BOINC data-directory...

Think the damage has already been done, the new client install having communicated to the servers. At any rate, look in the 6.2.19 client message log what the Data Dir path is. This is where all the files should be copied, off-line.

Such activities as this downgrading and client bit change from 32 >< 64 should be done:

1. With a back-up of the old data dir.
2. With the internet unplugged.

Only when satisfied, replug the internet connection.