Seems to be a Mac OS X problem. When launching a debugging session of an Eclipse project (not sure the weaving launcher is involved), it fails immediately. Adding `-XstartOnFirstThread` fixes the issue.

A few more pointers:

• the Equinox Weaving Launcher replaces the default Eclipse launch JVM command line arguments, instead of appending. The original arguments contain `-XstartOnFirstThread`
• when I try to reproduce this in a debugged VM, both the Scala launcher and the plain weaving launcher behave the same (don't work), which is consistent with the point above
• however, that is not the whole story: my Eclipse installation consistently works fine with the weaving launcher, but not with the Scala launcher.

While debugging I didn't notice any difference in the command line arguments passed to the JVM, but somehow the successful launch has `-XstartOnFirstThread` right after `java` (the first argument). That is weird, because it comes in before `-agentlib:...` (that is hard-coded in the standard launcher), while the normal launch configuration cmd arguments come after `agentlib`. This suggests some special treatment in the belly of Eclipse launchers that I could not dig out.

!MESSAGE Application error
!STACK 1
org.eclipse.swt.SWTException: Invalid thread access
	at org.eclipse.swt.SWT.error(SWT.java:4282)
	at org.eclipse.swt.SWT.error(SWT.java:4197)
	at org.eclipse.swt.SWT.error(SWT.java:4168)
	at org.eclipse.swt.widgets.Display.error(Display.java:1065)
	at org.eclipse.swt.widgets.Display.createDisplay(Display.java:822)
	at org.eclipse.swt.widgets.Display.create(Display.java:805)
	at org.eclipse.swt.graphics.Device.<init>(Device.java:130)
	at org.eclipse.swt.widgets.Display.<init>(Display.java:696)
	at org.eclipse.swt.widgets.Display.<init>(Display.java:687)
	at org.eclipse.ui.internal.Workbench.createDisplay(Workbench.java:716)
	at org.eclipse.ui.PlatformUI.createDisplay(PlatformUI.java:161)
	at org.eclipse.ui.internal.ide.application.IDEApplication.createDisplay(IDEApplication.java:153)
	at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:95)
	at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
	at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:110)
	at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:79)
	at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:344)
	at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:179)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)
	at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:622)
	at org.eclipse.equinox.launcher.Main.basicRun(Main.java:577)
	at org.eclipse.equinox.launcher.Main.run(Main.java:1410)
	at org.eclipse.equinox.launcher.Main.main(Main.java:1386)
An error has occurred. See the log file
/Users/dragos/Documents/runtime-New_configuration/.metadata/.log.