Why do I get an "invalid values" error when I try to access the network settings on Eclipse Mars?

I tried to access the eclipse marketplace and it failed, so I went to check the networking settings and got this:

If I continue the Network Connections tab does not load at first but after clicking off it and on it I can get it to load but Active Provider is blank:

I've tried restarting Eclipse, I get the same error.

I went to the workspace\.metadata\ folder and opened up the .log file, where I found the following:

!ENTRY org.eclipse.jface 4 2 2015-11-16 16:27:51.063
!MESSAGE Problems occurred when invoking code from plug-in: "org.eclipse.jface".
!STACK 0
java.lang.NullPointerException
    at org.eclipse.core.internal.net.StringUtil.split(StringUtil.java:33)
    at org.eclipse.core.internal.net.ProxyType.convertPropertyStringToHosts(ProxyType.java:102)
    at org.eclipse.core.internal.net.ProxyManager.getNonProxiedHosts(ProxyManager.java:118)
    at org.eclipse.core.internal.net.ProxySelector.getBypassHosts(ProxySelector.java:130)
    at org.eclipse.ui.internal.net.NonProxyHostsComposite.getProxyBypassData(NonProxyHostsComposite.java:344)
    at org.eclipse.ui.internal.net.NonProxyHostsComposite.initializeValues(NonProxyHostsComposite.java:283)
    at org.eclipse.ui.internal.net.NonProxyHostsComposite.createWidgets(NonProxyHostsComposite.java:133)
    at org.eclipse.ui.internal.net.NonProxyHostsComposite.<init>(NonProxyHostsComposite.java:66)
    at org.eclipse.ui.internal.net.ProxyPreferencePage.createNonProxiedHostsComposite(ProxyPreferencePage.java:89)
    at org.eclipse.ui.internal.net.ProxyPreferencePage.createContents(ProxyPreferencePage.java:55)
    at org.eclipse.jface.preference.PreferencePage.createControl(PreferencePage.java:241)
    at org.eclipse.jface.preference.PreferenceDialog.createPageControl(PreferenceDialog.java:1450)
    at org.eclipse.jface.preference.PreferenceDialog$13.run(PreferenceDialog.java:1217)
    at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
    at org.eclipse.ui.internal.JFaceUtil$1.run(JFaceUtil.java:50)
    at org.eclipse.jface.util.SafeRunnable.run(SafeRunnable.java:173)
    at org.eclipse.jface.preference.PreferenceDialog.showPage(PreferenceDialog.java:1209)
    at org.eclipse.ui.internal.dialogs.FilteredPreferenceDialog.showPage(FilteredPreferenceDialog.java:608)
    at org.eclipse.jface.preference.PreferenceDialog$9$1.run(PreferenceDialog.java:675)
    at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:70)
    at org.eclipse.jface.preference.PreferenceDialog$9.selectionChanged(PreferenceDialog.java:670)
    at org.eclipse.jface.viewers.StructuredViewer$3.run(StructuredViewer.java:877)
    at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
    at org.eclipse.ui.internal.JFaceUtil$1.run(JFaceUtil.java:50)
    at org.eclipse.jface.util.SafeRunnable.run(SafeRunnable.java:173)
    at org.eclipse.jface.viewers.StructuredViewer.firePostSelectionChanged(StructuredViewer.java:874)
    at org.eclipse.jface.viewers.StructuredViewer.handlePostSelect(StructuredViewer.java:1243)
    at org.eclipse.jface.viewers.StructuredViewer$5.widgetSelected(StructuredViewer.java:1269)
    at org.eclipse.jface.util.OpenStrategy.firePostSelectionEvent(OpenStrategy.java:265)
    at org.eclipse.jface.util.OpenStrategy.access$5(OpenStrategy.java:259)
    at org.eclipse.jface.util.OpenStrategy$1$2.run(OpenStrategy.java:440)
    at org.eclipse.swt.widgets.RunnableLock.run(RunnableLock.java:35)
    at org.eclipse.swt.widgets.Synchronizer.runAsyncMessages(Synchronizer.java:135)
    at org.eclipse.swt.widgets.Display.runAsyncMessages(Display.java:4155)
    at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3772)
    at org.eclipse.jface.window.Window.runEventLoop(Window.java:827)
    at org.eclipse.jface.window.Window.open(Window.java:803)
    at org.eclipse.ui.internal.dialogs.WorkbenchPreferenceDialog.open(WorkbenchPreferenceDialog.java:211)
    at org.eclipse.ui.internal.OpenPreferencesAction.run(OpenPreferencesAction.java:63)
    at org.eclipse.jface.action.Action.runWithEvent(Action.java:473)
    at org.eclipse.jface.action.ActionContributionItem.handleWidgetSelection(ActionContributionItem.java:595)
    at org.eclipse.jface.action.ActionContributionItem.access$2(ActionContributionItem.java:511)
    at org.eclipse.jface.action.ActionContributionItem$5.handleEvent(ActionContributionItem.java:420)
    at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
    at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4362)
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1113)
    at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:4180)
    at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3769)
    at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$4.run(PartRenderingEngine.java:1127)
    at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:337)
    at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1018)
    at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:156)
    at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:654)
    at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:337)
    at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:598)
    at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:150)
    at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:139)
    at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
    at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:134)
    at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:104)
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:380)
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:235)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:669)
    at org.eclipse.equinox.launcher.Main.basicRun(Main.java:608)
    at org.eclipse.equinox.launcher.Main.run(Main.java:1515)

Does anyone know a way to either fix or just work around this problem? Whether it's a matter of hacking the Eclipse config files or something I don't mind - I just need to get Eclipse online again!

Solution

Following the advice here I ran my eclipse with eclipse -clean and the properties window opened fine and I could access the marketplace. I restarted eclipse and everything was still working so it seems to have solved the problem.