I've read through the following threads, and didn't find anything that resolved my particular issue. I've restarted Boinc, restarted computers, checked my pref. files (and others). Was running fine this morning using both processors and crunching two wu's simultaneously, then I got a few minutes and decided to update version Berkeley BOINC 5.10.45 to 6.6.28.
Have not been able to do anything, including all items mentioned in those threads, to get Boinc to utilize both processors (run two tasks simultaneously). It sees them, just won't use #2 and there is no limit for just 1 in any of my preferences. Seti@Home global preferences set to "4" CPU's. Identical issues, two similar computers. Thanks for your time!

Boinc Only Recognizing 2 of 4 Cores
one project on dual core
Upgrading from BOINC 5.10.45 to 6.2.28

PC1 (currently running Rosetta & WCG)
PC2 (currently running ABC & AIS)

5/26/2009 11:38:01 AM Starting BOINC client version 6.6.28 for windows_intelx86
5/26/2009 11:38:01 AM log flags: task, file_xfer, sched_ops
5/26/2009 11:38:01 AM Libraries: libcurl/7.19.4 OpenSSL/0.9.8j zlib/1.2.3
5/26/2009 11:38:01 AM Data directory: C:\Documents and Settings\All Users\Application Data\BOINC
5/26/2009 11:38:01 AM Running under account ******
5/26/2009 11:38:01 AM Processor: 2 GenuineIntel Intel(R) Pentium(R) 4 CPU 3.60GHz [x86 Family 15 Model 4 Stepping 3]
5/26/2009 11:38:01 AM Processor features: fpu tsc pae nx sse sse2 mmx
5/26/2009 11:38:01 AM OS: Microsoft Windows XP: Professional x86 Edition, Service Pack 2, (05.01.2600.00)
5/26/2009 11:38:01 AM Memory: 1014.07 MB physical, 3.91 GB virtual
5/26/2009 11:38:01 AM Disk: 148.97 GB total, 133.84 GB free
5/26/2009 11:38:01 AM Local time is UTC -4 hours
5/26/2009 11:38:01 AM No CUDA devices found
5/26/2009 11:38:01 AM No coprocessors
5/26/2009 11:38:02 AM Not using a proxy
5/26/2009 11:38:02 AM rosetta@home URL: http://boinc.bakerlab.org/rosetta/; Computer ID: 850614; location: home; project prefs: default
5/26/2009 11:38:02 AM boincsimap URL: http://boinc.bio.wzw.tum.de/boincsimap/; Computer ID: 94899; location: (none); project prefs: default
5/26/2009 11:38:02 AM lhcathome URL: http://lhcathome.cern.ch/lhcathome/; Computer ID: 9671225; location: (none); project prefs: default
5/26/2009 11:38:02 AM orbit@home URL: http://orbit.psi.edu/oah/; Computer ID: 4233; location: (none); project prefs: default
5/26/2009 11:38:02 AM Pirates@Home URL: http://pirates.spy-hill.net/; Computer ID: 46316; location: (none); project prefs: default
5/26/2009 11:38:02 AM SETI@home URL: http://setiathome.berkeley.edu/; Computer ID: 4083921; location: work; project prefs: default
5/26/2009 11:38:02 AM Artificial Intelligence System URL: http://www.intelligencerealm.com/aisystem/; Computer ID: 11529; location: (none); project prefs: default
5/26/2009 11:38:02 AM World Community Grid URL: http://www.worldcommunitygrid.org/; Computer ID: 523243; location: (none); project prefs: default
5/26/2009 11:38:02 AM SETI@home General prefs: from SETI@home (last modified 26-May-2009 11:21:10)
5/26/2009 11:38:02 AM SETI@home Computer location: work
5/26/2009 11:38:02 AM SETI@home General prefs: no separate prefs for work; using your defaults
5/26/2009 11:38:02 AM Preferences limit memory usage when active to 557.74MB
5/26/2009 11:38:02 AM Preferences limit memory usage when idle to 963.36MB
5/26/2009 11:38:02 AM Preferences limit disk usage to 2.00GB
5/26/2009 11:38:02 AM Preferences limit # CPUs to 1

Seti@Home global preferences set to "4" CPU's

What about "On multiprocessors, use at most XX % of the processors (Enforced by version 6.1+)"?

95% of processors, 95% of CPU time, 55% of mem (in use), 95% of mem (not in use), 70% of pagefile; everything else is pretty much default

just goofy, huh?! I had changed it to 4 CPU's when I saw that "2" wasn't working - had binary math crashing through my brain.

The "On multiprocessors, use at most ...% of the processors" option is an integer number. When you set it to 95% on a 2 CPU machine, it will only use 1. Any number under 50% will use zero, any number between 50% and under 100% will use 1. 100% will use 2.

The "On multiprocessors, use at most .. processors" option is only used in BOINC 5.10 and below. It isn't used in BOINC 6.

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WOW ... and you have made my day once again!! I've read hundreds of your posts ... never thought we'd meet (well, electronically). These are my two work computers, so I will definitely update my preferences and check them in the morning!

Jord ... thank you! Well, it appears to be a simple fix, and at least I combined all common threads into one! I really wish there was a more complicated answer for all that work I put into the post, but I'll take it!

Any chance this can be added to the release notes for versions 6.x ... I know I jumped a couple versions, but this is a big change for a major version update.

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Number of usable CPUs has changed from 1 to 2. Running benchmarks.

That was it ... manually updated SAH project and it ran thru benchmarks, the fan kicked into high gear, and now crunching two tasks! Thanks again!