AD plugin reports following stack on windows with x64 jre. Consider shipping both x86 and x64 versions on com4j.dll and using correct one based on env.

http://java.net/projects/com4j/downloads

Nov 14, 2011 10:28:44 AM hudson.plugins.active_directory.ActiveDirectorySecurityRealm$DesciprotrImpl canDoNativeAuth
INFO: COM4J isn't working. Falling back to non-native authentication
java.lang.UnsatisfiedLinkError: C:\Users\build\.hudson\plugins\active-directory\WEB-INF\lib\com4j.dll: Can't load IA 32-bit .dll on a AMD 64-bit platform
at java.lang.ClassLoader$NativeLibrary.load(Native Method)
at java.lang.ClassLoader.loadLibrary0(ClassLoader.java:1928)
at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1825)
at java.lang.Runtime.load0(Runtime.java:792)
at java.lang.System.load(System.java:1059)
at com4j.COM4J.loadNativeLibrary(COM4J.java:430)
at com4j.COM4J.<clinit>(COM4J.java:386)
at com4j.typelibs.ado20.ClassFactory.createConnection(ClassFactory.java:13)
at hudson.plugins.active_directory.ActiveDirectorySecurityRealm$DesciprotrImpl.canDoNativeAuth(ActiveDirectorySecurityRealm.java:227)
at hudson.plugins.active_directory.ActiveDirectorySecurityRealm$DesciprotrImpl$canDoNativeAuth.call(Unknown Source)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:42)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:108)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:112)
at Script1.run(Script1.groovy:12)
at hudson.util.spring.BeanBuilder.parse(BeanBuilder.java:135)
at hudson.plugins.active_directory.ActiveDirectorySecurityRealm.createSecurityComponents(ActiveDirectorySecurityRealm.java:129)
at hudson.security.SecurityRealm.getSecurityComponents(SecurityRealm.java:398)
at hudson.security.HudsonFilter.reset(HudsonFilter.java:134)
at jenkins.model.Jenkins.setSecurityRealm(Jenkins.java:1916)
at jenkins.model.Jenkins$15.run(Jenkins.java:2397)
at org.jvnet.hudson.reactor.TaskGraphBuilder$TaskImpl.run(TaskGraphBuilder.java:146)
at org.jvnet.hudson.reactor.Reactor.runTask(Reactor.java:259)
at jenkins.model.Jenkins$5.runTask(Jenkins.java:798)
at org.jvnet.hudson.reactor.Reactor$2.run(Reactor.java:187)
at org.jvnet.hudson.reactor.Reactor$Node.run(Reactor.java:94)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
at java.lang.Thread.run(Thread.java:722)