I'm experiencing the same thing (although a previous install of 4.6.4 still works). I noticed the following in /Applications/SoapUI-5.0.0.app/Contents/java/app/bin/error.log
Exception in thread "AWT-EventQueue-0" java.lang.ExceptionInInitializerError
at com.eviware.soapui.DefaultSoapUICore.initSettings(DefaultSoapUICore.java:396)
at com.eviware.soapui.SwingSoapUICore.initSettings(SwingSoapUICore.java:122)
at com.eviware.soapui.DefaultSoapUICore.init(DefaultSoapUICore.java:148)
at com.eviware.soapui.StandaloneSoapUICore.<init>(StandaloneSoapUICore.java:40)
at com.eviware.soapui.SoapUI$SoapUIRunner.run(SoapUI.java:697)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:733)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:694)
at java.awt.EventQueue$3.run(EventQueue.java:692)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:703)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)
Caused by: java.lang.NullPointerException: ProxySelector must not be null.
at com.btr.proxy.selector.whitelist.ProxyBypassListSelector.<init>(ProxyBypassListSelector.java:39)
at com.btr.proxy.selector.whitelist.ProxyBypassListSelector.<init>(ProxyBypassListSelector.java:54)
at com.btr.proxy.search.desktop.osx.OsxProxySearchStrategy.installExceptionList(OsxProxySearchStrategy.java:224)
at com.btr.proxy.search.desktop.osx.OsxProxySearchStrategy.buildSelector(OsxProxySearchStrategy.java:141)
at com.btr.proxy.search.desktop.osx.OsxProxySearchStrategy.getProxySelector(OsxProxySearchStrategy.java:113)
at com.btr.proxy.search.desktop.DesktopProxySearchStrategy.getProxySelector(DesktopProxySearchStrategy.java:34)
at com.btr.proxy.search.ProxySearch.getProxySelector(ProxySearch.java:193)
at com.eviware.soapui.impl.wsdl.support.http.ProxyUtils.setGlobalProxy(ProxyUtils.java:201)
at com.eviware.soapui.impl.wsdl.support.http.HttpClientSupport.<clinit>(HttpClientSupport.java:63)
... 19 more