View Report as ODT not working (Report with an eventhandler)

Migrateduser

Hello
I am running Eclipse Mars.1 with BIRT 4.5.0.
I have a report with a table and a DataSet. In one cell I have an eventhandler
called "LatLonToLonLat". If I start a report preview with "View Report - View Report as ODT" I got the following error:
- the browser opens with an error message "Error: File not found ..."
- Error Log:
Error for "/viewer/preview"
java.lang.NoClassDefFoundError: org/apache/log4j/Logger
at com.eads.fo.birt.eventhandler.LatLonToLonLat.(LatLonToLonLat.java:30)
...
If I delete the eventhandler in the report, the preview is ok.

How can I fix this?