NoClassDefFoundError creating a mockup with plugin 1.6.45 for Confluence 2.9.2

Hi,
I use Mockup 1.6.45 with Confluence 2.9.2.
When I try to "save and close" a mockup I'm adding, I get a NoClassDefFoundError

javax.servlet.ServletException: L'execution de la servlet a lance une exception
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:313)

caused by: java.lang.NoClassDefFoundError: org/directwebremoting/WebContextFactory

at org.randombits.confluence.support.DWRServletProvider.getRequest(DWRServletProvider.java:28)

Someone could help me on that issue please ?

Math