Eclipse Marketplace not visible

Eclipse marketplace was not installed initially. Then I followed instructions here on SO and I restarted Eclipse several times in the meanwhile.

I have set up the Internet Proxy already (I needed to do so to install the Marketplace itself).

But still the Marketplace is not visible under the Help menu. I can also not start installations via Marketplace Drag-to-install buttons.

When I run eclipse -console I get the following messages, which I believe are not related to the problem:

org.eclipse.m2e.logback.configuration: The org.eclipse.m2e.logback.configuration bundle was activated before the state location was initialized.  Will retry after the state location is initialized.

osgi> org.eclipse.m2e.logback.configuration: Logback config file: C:\Users\___\workspace\tests\.metadata\.plugins\org.eclipse.m2e.logback.configuration\logback.1.5.0.20140606-0033.xml
org.eclipse.m2e.logback.configuration: Initializing logback
java.lang.ClassCastException: org.eclipse.osgi.internal.framework.EquinoxConfiguration$1 cannot be cast to java.lang.String
        at org.eclipse.m2e.logback.configuration.LogHelper.logJavaProperties(LogHelper.java:26)
        at org.eclipse.m2e.logback.configuration.LogPlugin.loadConfiguration(LogPlugin.java:189)
        at org.eclipse.m2e.logback.configuration.LogPlugin.configureLogback(LogPlugin.java:144)
        at org.eclipse.m2e.logback.configuration.LogPlugin.access$2(LogPlugin.java:107)
        at org.eclipse.m2e.logback.configuration.LogPlugin$1.run(LogPlugin.java:62)
        at java.util.TimerThread.mainLoop(Unknown Source)
        at java.util.TimerThread.run(Unknown Source)

I have read most of the "Question that may already have your answer" which were suggested by SO while writing this question, still no luck.

I'm working on Eclipse Luna SR1 4.4.1 on Windows 7 SP1 x64.

What else could I do to get the Eclipse Marketplace into my installation?