The Xtext update site is needed in order to obtain the required version 2.9 as the Eclipse Mars update site only has version 2.8.4.
Go to Help -> Install New Software., and add each of the following update sites (by clicking on the Add. Installing required development features Adding required update sites There are several possible ways to make a development environment to work on PapyrusRT, but it's a good idea to follow the steps provided here as we know these work.
