I am seeing the exact same error in the error.log. In the DOS command window I see the following trace. Note that I've tried setting GRE_HOME=%GROOVY_HOME%, and %GROOVY_HOME%\bin; neither works.
Configuring log4j from [C:\Program Files\eviware\soapui-pro-3.6-beta2\bin\soapui-log4j.xml]
13:56:14,803 INFO [DefaultSoapUICore] initialized soapui-settings from [...]
13:56:14,834 INFO [DefaultSoapUICore] Adding listeners from [C:\Program Files\eviware\soapui-pro-3.6-beta2\bin\listeners\demo-listeners.xml]
Configuring log4j from [C:\Program Files\eviware\soapui-pro-3.6-beta2\bin\soapui-log4j.xml]
13:56:15,912 INFO [DefaultSoapUICore] initialized soapui-settings from [...]
13:56:16,709 WARN [SoapUIProGroovyScriptEngineFactory] Missing scripts folder [C:\Program Files\eviware\soapUI-Pro-3.5\bin\scripts]
13:56:16,725 INFO [DefaultSoapUICore] Adding listeners from [C:\Program Files\eviware\soapui-pro-3.6-beta2\bin\listeners\demo-listeners.xml]
13:56:18,959 INFO [WorkspaceImpl] Loading workspace from [...]
13:56:20,662 INFO [WsdlProject] Loaded project from [...REST-API-Coverage-soapui-project.xml]
13:56:25,459 INFO [SoapUI] Used java version: 1.6.0_20
13:56:30,444 INFO [DefaultSoapUICore] Adding actions from [C:\Program Files\eviware\soapui-pro-3.6-beta2\bin\actions\demo-actions.xml]
Exception in thread "XpcMessageLoop" java.lang.RuntimeException: java.io.FileNotFoundException: GRE_HOME doesn't exist
at com.teamdev.xpcom.a.a(Unknown Source)
at com.teamdev.xpcom.b$b.run(Unknown Source)
Caused by: java.io.FileNotFoundException: GRE_HOME doesn't exist
at org.mozilla.xpcom.Mozilla.getGREPathWithProperties(Mozilla.java:148)
... 2 more
org.mozilla.xpcom.XPCOMInitializationException: Must call Mozilla.getInstance().initialize() before using this method
at org.mozilla.xpcom.Mozilla.getServiceManager(Mozilla.java:869)
at com.teamdev.xpcom.util.ProxyManager.<init>(Unknown Source)
at com.teamdev.xpcom.util.ProxyManager.getInstance(Unknown Source)
at com.teamdev.xpcom.b.invokeLater(Unknown Source)
at com.teamdev.xpcom.Xpcom.invokeLater(Unknown Source)
at com.teamdev.jxbrowser1.impl.a.a.<init>(Unknown Source)
at com.teamdev.jxbrowser1.console.ConsoleService.getConsoleService(Unknown Source)
at com.teamdev.jxbrowser.mozilla.MozillaScriptErrorWatcher.<init>(Unknown Source)
at com.teamdev.jxbrowser.mozilla.MozillaScriptErrorWatcher.getInstance(Unknown Source)
at com.teamdev.jxbrowser.mozilla.MozillaBrowserFactory.<init>(Unknown Source)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
at java.lang.Class.newInstance0(Class.java:355)
at java.lang.Class.newInstance(Class.java:308)
at com.teamdev.jxbrowser.BrowserFactory$a.a(Unknown Source)
at com.teamdev.jxbrowser.BrowserFactory.createBrowser(Unknown Source)
at com.eviware.soapui.support.components.BrowserComponent.initBrowser(BrowserComponent.java:512)
at com.eviware.soapui.support.components.BrowserComponent.getComponent(BrowserComponent.java:186)
at com.eviware.soapui.ui.URLDesktopPanel.<init>(URLDesktopPanel.java:38)
at com.eviware.soapui.SoapUI.showPushPage(SoapUI.java:1237)
at com.eviware.soapui.SoapUI$3.run(SoapUI.java:788)
[bunch of java.awt.EventDispatch stuff]
Caused by: java.lang.NullPointerException
at org.mozilla.xpcom.Mozilla.getServiceManager(Mozilla.java:867)
... 30 more