due to the junit changes in eclipse 3.6.0 version, which birt 2.6.0 is based on:
http://wiki.eclipse.org/eclipse/testing/junit4_changes 


please update the related junit test plugins to use correct junit version range in the manifest.mf:
require-bundle: org.eclipse.birt.core;bundle-version="[2.1.0,3.0.0)",o^m
 rg.eclipse.birt.report.engine;bundle-version="[2.1.0,3.0.0)",org.ecli^m
 pse.birt.data;bundle-version="[2.1.0,3.0.0)",com.lowagie.itext,org.ec^m
 lipse.birt.report.data.adapter;bundle-version="[2.1.0,3.0.0)",org.ecl^m
 ipse.birt.report.engine.emitter.postscript;bundle-version="[2.1.0,3.0^m
 .0)",org.junit;bundle-version="[3.8.1,4.0.0)";resolution:=optional;vi^m
 sibility:=reexport


 if you still want to be able to run with junit3, use a range of "3.8.0". if you only want to run on junit4, you can use a range of "4.7.0".
including:

org.eclipse.birt.core.tests_2.5.2.v20100303-0630
org.eclipse.birt.report.engine.emitter.html.tests_2.5.2.v20100303-0630
org.eclipse.birt.report.engine.emitter.pdf.tests_2.5.2.v20100303-0630
org.eclipse.birt.report.engine.tests_2.5.2.v20100303-0630
fixed the problem.
verified in daily build 201003120943.

bug closed.