Error writing workspace state file

Todays maven problem is a m2eclipse problem. Somehow I get 'Error writing workspace state file' which leaves me in a workspace which doesn't properly update anymore.

org.eclipse.core.runtime.CoreException: Could not read maven project
 at org.maven.ide.eclipse.internal.project.MavenProjectFacade.getMavenProject(MavenProjectFacade.java:190)
 at org.maven.ide.eclipse.internal.project.WorkspaceStateWriter.mavenProjectChanged(WorkspaceStateWriter.java:52)
 at org.maven.ide.eclipse.internal.project.MavenProjectManagerImpl.notifyProjectChangeListeners(MavenProjectManagerImpl.java:698)
 at org.maven.ide.eclipse.internal.project.MavenProjectManagerImpl.refresh(MavenProjectManagerImpl.java:366)
 at org.maven.ide.eclipse.internal.project.MavenProjectManagerRefreshJob.run(MavenProjectManagerRefreshJob.java:95)
 at org.eclipse.core.internal.jobs.Worker.run(Worker.java:55)
Contains: Cannot resolve pre-scanned extension artifact: org.apache.maven.wagon:wagon-scm: Failed to resolve extension: org.apache.maven.wagon:wagon-scm:jar:1.0-beta-6
org.apache.maven.extension.ExtensionScanningException: Cannot resolve pre-scanned extension artifact: org.apache.maven.wagon:wagon-scm: Failed to resolve extension: org.apache.maven.wagon:wagon-scm:jar:1.0-beta-6
 at org.apache.maven.extension.DefaultBuildExtensionScanner.checkModelBuildForExtensions(DefaultBuildExtensionScanner.java:369)
 at org.apache.maven.extension.DefaultBuildExtensionScanner.scanInternal(DefaultBuildExtensionScanner.java:187)
 at org.apache.maven.extension.DefaultBuildExtensionScanner.scanForBuildExtensions(DefaultBuildExtensionScanner.java:120)
 at org.apache.maven.embedder.MavenEmbedder.readProject(MavenEmbedder.java:377)
 at org.apache.maven.embedder.MavenEmbedder.readProjectWithDependencies_aroundBody0(MavenEmbedder.java:416)
 at org.apache.maven.embedder.MavenEmbedder.readProjectWithDependencies_aroundBody1$advice(MavenEmbedder.java:304)
 at org.apache.maven.embedder.MavenEmbedder.readProjectWithDependencies(MavenEmbedder.java:1)
 at org.maven.ide.eclipse.internal.project.MavenProjectManagerImpl$MavenProjectReader.execute(MavenProjectManagerImpl.java:1117)
 at org.maven.ide.eclipse.internal.project.MavenProjectManagerImpl.execute(MavenProjectManagerImpl.java:986)
 at org.maven.ide.eclipse.internal.project.MavenProjectManagerImpl.readProjectWithDependencies(MavenProjectManagerImpl.java:967)
 at org.maven.ide.eclipse.internal.project.MavenProjectFacade.getMavenProject(MavenProjectFacade.java:180)
 at org.maven.ide.eclipse.internal.project.WorkspaceStateWriter.mavenProjectChanged(WorkspaceStateWriter.java:52)
 at org.maven.ide.eclipse.internal.project.MavenProjectManagerImpl.notifyProjectChangeListeners(MavenProjectManagerImpl.java:698)
 at org.maven.ide.eclipse.internal.project.MavenProjectManagerImpl.refresh(MavenProjectManagerImpl.java:366)
 at org.maven.ide.eclipse.internal.project.MavenProjectManagerRefreshJob.run(MavenProjectManagerRefreshJob.java:95)
 at org.eclipse.core.internal.jobs.Worker.run(Worker.java:55)
Caused by: org.apache.maven.extension.ExtensionManagerException: Failed to resolve extension: org.apache.maven.wagon:wagon-scm:jar:1.0-beta-6
 at org.apache.maven.extension.DefaultExtensionManager.init$_aroundBody2(DefaultExtensionManager.java:352)
 at org.apache.maven.extension.DefaultExtensionManager.init$_aroundBody3$advice(DefaultExtensionManager.java:384)
 at org.apache.maven.extension.DefaultExtensionManager.addExtension(DefaultExtensionManager.java:352)
 at org.apache.maven.extension.DefaultExtensionManager.addExtension(DefaultExtensionManager.java:148)
 at org.apache.maven.extension.DefaultBuildExtensionScanner.checkModelBuildForExtensions(DefaultBuildExtensionScanner.java:365)
 ... 15 more