Maven build fails at openHAB Model Script

Hi,
I tried to build openHAB with eclipse according to the instruction on the Wiki (Pure Eclipse).
The build fails with the following error at openHAB Model Script.
Any idea what is wrong? I am using JDK 1.7 and maven 3.3.3

[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 09:43 min
[INFO] Finished at: 2015-11-09T13:34:48+01:00
[INFO] Final Memory: 401M/1520M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.eclipse.tycho:tycho-compiler-plugin:0.22.0:compile (default-compile) on project org.openhab.model.script: Compilation failure: Compilation failure:
[ERROR] C:\Users\myuser\Documents\openhab\source\openhab\bundles\model\org.openhab.model.script\xtend-gen\org\openhab\model\script\jvmmodel\ScriptJvmModelInferrer.java:[7]
[ERROR] import org.eclipse.xtext.xbase.lib.Extension;
[ERROR] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[ERROR] The import org.eclipse.xtext.xbase.lib.Extension cannot be resolved
[ERROR] C:\Users\myuser\Documents\openhab\source\openhab\bundles\model\org.openhab.model.script\xtend-gen\org\openhab\model\script\jvmmodel\ScriptJvmModelInferrer.java:[21]
[ERROR] @Extension
[ERROR] ^^^^^^^^^
[ERROR] Extension cannot be resolved to a type
[ERROR] C:\Users\myuserDocuments\openhab\source\openhab\bundles\model\org.openhab.model.script\xtend-gen\org\openhab\model\script\jvmmodel\ScriptJvmModelInferrer.java:[25]
[ERROR] @Extension
[ERROR] ^^^^^^^^^
[ERROR] Extension cannot be resolved to a type
[ERROR] 3 problems (3 errors)
[ERROR] -> [Help 1]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoFailureException
[ERROR]
[ERROR] After correcting the problems, you can resume the build with the command
[ERROR] mvn -rf :org.openhab.model.script