If you manually move your BEA installation directory somewhere else, the WebLogic server will fail to start with a license exception. Further digging will reveal that it is looking for the license file, license.bea, in the old directory.
WebLogic 8.1 seems to use a hard-coded pathname to the license file. I could not find where it was hard-coded -- it was not in any of the generated start-up scripts. Their installer must put it into a JAR somewhere, or maybe even compile up a class file that contains it. There is, however, a work-around. Add the following system property to the command that starts the WLS server:
Of course, to have a hope of this working, you must edit the various BEA scripts to point to the new directory as well (or, a novel thought, to use relative pathnames).