if I select Enable security > Unix user/group database, i'm unable to log into hudson. tried serveral system accounts - am able to ssh to the server using the login/password of the account but unable to log into hudson:

Invalid login information. Please try again.

/var/log/hudson/hudson.log:

Jul 14, 2010 10:52:41 PM hudson.security.AuthenticationProcessingFilter2 onUnsuccessfulAuthentication
INFO: Login attempt failed
org.acegisecurity.BadCredentialsException: pam_authenticate failed : Authentication failure; nested exception is org.jvnet.libpam.PAMException: pam_authenticate failed : Authentication failure
at hudson.security.PAMSecurityRealm$PAMAuthenticationProvider.authenticate(PAMSecurityRealm.java:100)
at org.acegisecurity.providers.ProviderManager.doAuthentication(ProviderManager.java:195)
at org.acegisecurity.AbstractAuthenticationManager.authenticate(AbstractAuthenticationManager.java:45)
at org.acegisecurity.ui.webapp.AuthenticationProcessingFilter.attemptAuthentication(AuthenticationProcessingFilter.java:71)
at org.acegisecurity.ui.AbstractProcessingFilter.doFilter(AbstractProcessingFilter.java:252)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at org.acegisecurity.ui.basicauth.BasicProcessingFilter.doFilter(BasicProcessingFilter.java:173)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at org.acegisecurity.context.HttpSessionContextIntegrationFilter.doFilter(HttpSessionContextIntegrationFilter.java:249)
at hudson.security.HttpSessionContextIntegrationFilter2.doFilter(HttpSessionContextIntegrationFilter2.java:66)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at hudson.security.ChainedServletFilter.doFilter(ChainedServletFilter.java:76)
at hudson.security.HudsonFilter.doFilter(HudsonFilter.java:164)
at winstone.FilterConfiguration.execute(FilterConfiguration.java:195)
at winstone.RequestDispatcher.doFilter(RequestDispatcher.java:368)
at winstone.RequestDispatcher.forward(RequestDispatcher.java:333)
at winstone.RequestHandlerThread.processRequest(RequestHandlerThread.java:244)
at winstone.RequestHandlerThread.run(RequestHandlerThread.java:150)
at java.lang.Thread.run(Thread.java:636)
Caused by: org.jvnet.libpam.PAMException: pam_authenticate failed : Authentication failure
at org.jvnet.libpam.PAM.check(PAM.java:105)
at org.jvnet.libpam.PAM.authenticate(PAM.java:123)
at hudson.security.PAMSecurityRealm$PAMAuthenticationProvider.authenticate(PAMSecurityRealm.java:90)
... 18 more