If you are getting an error like this:
java.lang.RuntimeException: There were errors initializing your configuration: com.solarmetric.license.LicenseException: Your license key "376D-896F-8B43-BE3D-3D00" expired on "5/14/07 5:00 PM". Please contact email@example.com for purchase or evaluation information.
...this is a known bug. This will affect you only if you downloaded WebLogic 10 before May 14, as I did. You need to get the patch from BEA or you'll never be able to start WebLogic. Just go through the process of getting the evaluation copy again, and they'll give you some options. Hopefully this saves a few headaches.