From the Struts download page:
Log4J Users Please Note - A packaging error has been
uncovered that caused the copy of
in the Struts 1.1 Beta 2 release to be built incorrectly. If you are using
Log4J for your logging needs, you will need to download the Commons Logging
1.0.1 release (convenient links are provided in the
logging directory) and replace your copy of
commons-logging.jar with the one found in the 1.0.1 release.