You need a 64-bit trio:

• 64-bit OS
• 64-bit Java
• 64-bit Eclipse

Working pairings of OS, JDK and Eclipse:

• 32-bit OS | 32-bit JDK | 32-bit Eclipse (32-bit only)
• 64-bit OS | 32-bit JDK | 32-bit Eclipse
• 64-bit OS | 64-bit JDK | 64bit Eclipse (64-bit only)

I had several JDKs and JREs installed.

Each of them had their own entry in the PATH variable, all was working more or less.

Judging from the PATH variables, some installations were completely useless, since they were never used. Of course, the "inactive" Javas could be referenced manually from within Eclipse if I needed, but I never did that, so I really did not need them. (At least I thought so at that time...)

I cleaned up the mess, deinstalled all current Java's, installed only JDK + JRE 1.7 64-bit.

One of the Eclipse 'installations' failed afterwards with the Failed to Load the JNI shared Library and a given path relative to the fresh installed JDK where it thought the jvm.dll to be.

The failing Eclipse was the only one of all my IDEs that was still a 32-bit version on my otherwise all-64-bit setup.

Adding VM arguments, like so often mentioned, in the eclipse.ini was no use in my case (because I had only the wrong JDK/JRE to relate to.)

I was also unable to find out how to check if this Eclipse was a 32-bit or 64-bit version (I could not look it up in the Task Manager, since this Eclipse 'installation' would not start up. And since it had been a while since I had set it up, I could not remember its version either.)

In case you use a newer JDK and a older JRE you might be in for trouble, too, but then it is more likely a java.lang.UnsupportedClassVersionError appears, IIRC.

Make sure your eclipse.ini file includes the following lines.

-vmC:\path\to\64bit\java\bin\javaw.exe

My eclipse.ini for example:

-startupplugins/org.eclipse.equinox.launcher_1.1.1.R36x_v20101122_1400.jar--launcher.libraryplugins/org.eclipse.equinox.launcher.win32.win32.x86_64_1.1.2.R36x_v20101222-productorg.eclipse.epp.package.java.product--launcher.defaultActionopenFile--launcher.XXMaxPermSize256M-showsplashorg.eclipse.platform-vmC:\Program Files\Java\jdk1.6.0_32\bin\javaw.exe--launcher.XXMaxPermSize256m--launcher.defaultActionopenFile-vmargs-Dosgi.requiredJavaVersion=1.5-Xms40m-Xmx512m

Use OS and Eclipse both 64 bit or both 32 bit keep same and config eclipse.ini.

Your eclipse.ini file can be found in your eclipse folder.