I cannot see the full error message in your post (after the Problem Report).
As mentioned in the post Unit tests with Mockito - #2 by tdelhomenie the version of the plugin to skip must match with the version used by the build type (com.is2t.easyant.buildtypes:build-microej-javalib:6.2.+). For this build type version, the microej-testsuite version is 4.2.+, so it should be:
<ea:property name="skip.com.is2t.easyant.plugins#microej-testsuite;4.2.+" value="true" />
You should see a trace saying that the plugin has been skipped.