我已经为Liferay Service Builder创建了一个配置。在此之后我尝试构建服务，但是我收到了以下错误：
Buildfile: C:\LiferayNew\liferay-plugins-sdk-6.2\portlets\guestbook-portlet\build.xml
BUILD FAILED
C:\LiferayNew\liferay-plugins-sdk-6.2\portlets\guestbook-portlet\build.xml:5: The following error occurred while executing this line:
C:\LiferayNew\liferay-plugins-sdk-6.2\portlets\build-common-portlet.xml:5: The following error occurred while executing this line:
C:\LiferayNew\liferay-plugins-sdk-6.2\build-common-plugin.xml:5: The following error occurred while executing this line:
C:\LiferayNew\liferay-plugins-sdk-6.2\build-common.xml:60: The following error occurred while executing this line:
C:\LiferayNew\liferay-plugins-sdk-6.2\build-common-ivy.xml:71: The following error occurred while executing this line:
C:\LiferayNew\liferay-plugins-sdk-6.2\build-common-ivy.xml:55: java.net.MalformedURLException: no protocol: ${ivy.jar.url}
Total time: 1 second.
我如何解决这个问题？