Apparently if a project and its issues are deleted, some of the portlets break. In 2.4.1 this prevents the user logging in:

java.lang.NullPointerException
at
org.apache.jasper.runtime.JspRuntimeLibrary.getContextRelativePath(JspRu
ntimeLibrary.java:774)
at
org.apache.jasper.runtime.JspRuntimeLibrary.include(JspRuntimeLibrary.ja
va:819)
at
org.apache.jsp.dashboard_jsp._jspService(dashboard_jsp.java:131)
....