I fill this page correctly to have a slave :
http://my.server/hudson/computer/createItem

then when I submit the form, I have this error :
java.lang.Error: This page expects a form submission.

So, I cannot add any slave.

I have the same bug on Hudson 1.288 and 1.287.
I tried with IE 6 and Firefox 3 with same result.
I am on Windows XP SP 2.

Stacktrace :

org.kohsuke.stapler.RequestImpl.getSubmittedForm(RequestImpl.java:674)
hudson.model.ComputerSet.doDoCreateItem(ComputerSet.java:220)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
java.lang.reflect.Method.invoke(Unknown Source)
org.kohsuke.stapler.Function$InstanceFunction.invoke(Function.java:156)
org.kohsuke.stapler.Function.bindAndInvoke(Function.java:76)
org.kohsuke.stapler.MetaClass$1.doDispatch(MetaClass.java:73)
org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:30)
org.kohsuke.stapler.Stapler.invoke(Stapler.java:438)
org.kohsuke.stapler.MetaClass$4.doDispatch(MetaClass.java:145)
org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:30)
org.kohsuke.stapler.Stapler.invoke(Stapler.java:438)
org.kohsuke.stapler.Stapler.invoke(Stapler.java:356)
org.kohsuke.stapler.Stapler.service(Stapler.java:116)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:91)
hudson.util.PluginServletFilter.doFilter(PluginServletFilter.java:83)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:75)
hudson.security.UnwrapSecurityExceptionFilter.doFilter(UnwrapSecurityExceptionFilter.java:51)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:78)
org.acegisecurity.ui.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:166)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:78)
org.acegisecurity.providers.anonymous.AnonymousProcessingFilter.doFilter(AnonymousProcessingFilter.java:125)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:78)
hudson.security.BasicAuthenticationFilter.doFilter(BasicAuthenticationFilter.java:112)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:78)
hudson.security.ChainedServletFilter.doFilter(ChainedServletFilter.java:67)
hudson.security.HudsonFilter.doFilter(HudsonFilter.java:133)