Jenkins / Maven: Could not resolve default JAVA_HOME path, Build failing

I’ve got a problem regarding Java Builds in Jenkins.

The Error I resolve is the following one:

Unable to locate the Javac Compiler in:
Please ensure you are using JDK 1.4 or above and
not a JRE (the class is required).
In most cases you can change the location of your Java
installation by setting the JAVA_HOME environment variable.

I got JDK1.6 and JDK1.7 projects, so I need two JDK installations. For my default Java JDK I used the 1.6 for the JAVA_HOME variable, which points to C:\Program Files\Java\jdk1.6.0_45. Same for the 1.7 version, but in a separated variable (JAVA_HOME7).
The PATH variable contains the appended \bin to the two JDK versions.

In Jenkins I also added both versions for JDK and as helper variables.
If I am setting a concrete version for a project (e.g. JDK1.7), then it’s building without any issues. Unfortunately I’ve got a lot of build-projects, so it would be time consuming to set this manually.

I don’t understand where the call or variable for the path of the error C:\Jenkins\jre\..\lib\tools.jar is set and where I can modify it…

Jenkins Version: 1.509.4

Any hints or advices how to solve this problem?

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