HorstSkoff,
Can you answer some more questions for me to understand the issue better ?
1) Can you share your build id from Help > About MyEclipse Enterprise Workbench ? Paste it here.
2) Clear the contents of the .log file which is located at <workspace dir>/.metadata/.log and now replicate the issue. Copy paste the contents of the .log file here .
3) Can you please list out steps in detail right from project creation to UML2 class generation for me to be able to replicate the issue at my end ?