Ok,

I think the general flow goes something like this. Firstly I tried to login to
Hudson and failed because it's Monday morning and I forgot the password. I
tried to login again using the correct username and password and was presented
with this page.

java.lang.StringIndexOutOfBoundsException: String index out of range: -7
java.lang.String.substring(String.java:1768)
java.lang.String.substring(String.java:1735)
hudson.security.AuthenticationProcessingFilter2.determineTargetUrl(AuthenticationProcessingFilter2.java:27)
org.acegisecurity.ui.AbstractProcessingFilter.successfulAuthentication(AbstractProcessingFilter.java:480)
org.acegisecurity.ui.AbstractProcessingFilter.doFilter(AbstractProcessingFilter.java:266)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:55)
org.acegisecurity.ui.basicauth.BasicProcessingFilter.doFilter(BasicProcessingFilter.java:173)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:55)
org.acegisecurity.context.HttpSessionContextIntegrationFilter.doFilter(HttpSessionContextIntegrationFilter.java:249)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:55)
hudson.security.ChainedServletFilter.doFilter(ChainedServletFilter.java:44)
hudson.security.HudsonFilter.doFilter(HudsonFilter.java:72)