Following my previous question (http://www.eclipse.org/forums/index.php/t/488109/) I updated my Xtext installation from 2.3 to 2.4 using the Eclipse update site. Then I tried to generate Xtext artifacts for one of the existing projects and I got some errors during the process. Here is a summary (a full log is attached):
warning(200): ../xtext.jdbc/src-gen/xtext/parser/antlr/internal/InternalJdbc.g:5671:1: Decision can match input such as "RULE_ID" using multiple alternatives: 2, 3
As a result, alternative(s) 3 were disabled for that input
error(201): ../xtext.jdbc/src-gen/xtext/parser/antlr/internal/InternalJdbc.g:5671:1: The following alternatives can never be matched: 3
31626 [main] ERROR enerator.CompositeGeneratorFragment - java.io.FileNotFoundException: ../xtext.jdbc/src-gen/xtext/parser/antlr/internal/InternalJdbcLexer.java (No such file or directory)
org.eclipse.emf.common.util.WrappedException: java.io.FileNotFoundException: ../xtext.jdbc/src-gen/xtext/parser/antlr/internal/InternalJdbcLexer.java (No such file or directory)
the error message states that there is a case where the parser has read a part of its input model, and needs to decide which decision to take (e.g. optional element or a real choice described with the '|' symbol), but cannot by looking at the next few characters.
This could happen because the Xbase grammar changed below your grammar, and introduced a conflict.
I cannot say anything more without seeing the entire grammar, but hope it helps,