When Tycho tries to resolve the whole jboss tools reactor, it fails while trying to read BREE for org.maven.ide.eclipse.wtp.overlay.ui-0.14.0.20110928-2045
Indeed, this BREE is set to a concatenation of several BREE.

See error:
[INFO] Resolving class path of MavenProject: org.jboss.tools.examples:examples.site:1.2.1-SNAPSHOT @ /home/istria/workspaces/workspaceJBossTycho/jboss-tycho/examples/site/pom.xml
[INFO] Computing target platform for MavenProject: org.jboss.tools.maven.features:org.jboss.tools.maven.feature:1.3.0-SNAPSHOT @ /home/istria/workspaces/workspaceJBossTycho/jboss-tycho/maven/features/org.jboss.tools.maven.feature/pom.xml
[INFO] Adding repository (cached) http://download.jboss.org/jbosstools/updates/target-platform_3.3.indigo.SR1-M/latest/
[INFO] Resolving dependencies of MavenProject: org.jboss.tools.maven.features:org.jboss.tools.maven.feature:1.3.0-SNAPSHOT @ /home/istria/workspaces/workspaceJBossTycho/jboss-tycho/maven/features/org.jboss.tools.maven.feature/pom.xml
[INFO] Downloading org.eclipse.equinox.p2.discovery
[INFO] Fetching org.eclipse.equinox.p2.discovery_1.0.100.v20110502-1955.jar (0B of 34,61kB at 0B/s) from http://download.jboss.org/jbosstools/updates/target-platform_3.3.indigo.SR1-M/latest/plugins/
...sic...
[INFO] 1 operation remaining.
[INFO] Fetching org.maven.ide.eclipse.wtp.feature_0.14.0.20110928-2045.jar (3,25kB of 3,25kB at 0B/s) from http://download.jboss.org/jbosstools/updates/target-platform_3.3.indigo.SR1-M/latest/features/
[INFO] Downloading org.sonatype.m2e.mavenarchiver.feature
[INFO] Fetching org.sonatype.m2e.mavenarchiver.feature_0.15.0.201109290002.jar (0B of 11,82kB at 0B/s) from http://download.jboss.org/jbosstools/updates/target-platform_3.3.indigo.SR1-M/latest/features/
[INFO] 1 operation remaining.
[INFO] Fetching org.sonatype.m2e.mavenarchiver.feature_0.15.0.201109290002.jar (4kB of 11,82kB at 0B/s) from http://download.jboss.org/jbosstools/updates/target-platform_3.3.indigo.SR1-M/latest/features/
[INFO] Resolving class path of MavenProject: org.jboss.tools.maven.features:org.jboss.tools.maven.feature:1.3.0-SNAPSHOT @ /home/istria/workspaces/workspaceJBossTycho/jboss-tycho/maven/features/org.jboss.tools.maven.feature/pom.xml
[ERROR] Internal error: org.eclipse.tycho.core.osgitools.OsgiManifestParserException: Exception parsing OSGi MANIFEST /home/istria/.m2/repository/p2/osgi/bundle/org.maven.ide.eclipse.wtp.overlay.ui/0.14.0.20110928-2045/org.maven.ide.eclipse.wtp.overlay.ui-0.14.0.20110928-2045.jar!/META-INF/MANIFEST.MF: null: UnknownEnvironmentException -> [Help 1]
org.apache.maven.InternalErrorException: Internal error: org.eclipse.tycho.core.osgitools.OsgiManifestParserException: Exception parsing OSGi MANIFEST /home/istria/.m2/repository/p2/osgi/bundle/org.maven.ide.eclipse.wtp.overlay.ui/0.14.0.20110928-2045/org.maven.ide.eclipse.wtp.overlay.ui-0.14.0.20110928-2045.jar!/META-INF/MANIFEST.MF: null
at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:168)
at org.apache.maven.cli.MavenCli.execute(MavenCli.java:537)
at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:196)
at org.apache.maven.cli.MavenCli.main(MavenCli.java:141)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:290)
at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:230)
at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:409)
at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:352)
Caused by: org.eclipse.tycho.core.osgitools.OsgiManifestParserException: Exception parsing OSGi MANIFEST /home/istria/.m2/repository/p2/osgi/bundle/org.maven.ide.eclipse.wtp.overlay.ui/0.14.0.20110928-2045/org.maven.ide.eclipse.wtp.overlay.ui-0.14.0.20110928-2045.jar!/META-INF/MANIFEST.MF: null
at org.eclipse.tycho.core.osgitools.OsgiManifest.parseExecutionEnvironments(OsgiManifest.java:64)
at org.eclipse.tycho.core.osgitools.OsgiManifest.<init>(OsgiManifest.java:48)
at org.eclipse.tycho.core.osgitools.OsgiManifest.parse(OsgiManifest.java:140)
at org.eclipse.tycho.core.osgitools.DefaultBundleReader.loadManifestFromFile(DefaultBundleReader.java:90)
at org.eclipse.tycho.core.osgitools.DefaultBundleReader.doLoadManifest(DefaultBundleReader.java:67)
at org.eclipse.tycho.core.osgitools.DefaultBundleReader.loadManifest(DefaultBundleReader.java:56)
at org.eclipse.tycho.core.maven.MavenDependencyInjector.getClasspathElements(MavenDependencyInjector.java:139)
at org.eclipse.tycho.core.maven.MavenDependencyInjector.newExternalDependencies(MavenDependencyInjector.java:110)
at org.eclipse.tycho.core.maven.MavenDependencyInjector.addDependency(MavenDependencyInjector.java:93)
at org.eclipse.tycho.core.maven.MavenDependencyInjector.injectMavenDependencies(MavenDependencyInjector.java:49)
at org.eclipse.tycho.p2.resolver.P2TargetPlatformResolver.injectDependenciesIntoMavenModel(P2TargetPlatformResolver.java:546)
at org.eclipse.tycho.core.resolver.DefaultTychoDependencyResolver.resolveProject(DefaultTychoDependencyResolver.java:113)
at org.eclipse.tycho.core.maven.TychoMavenLifecycleParticipant.afterProjectsRead(TychoMavenLifecycleParticipant.java:61)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:273)
at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:156)
... 11 more
Caused by: org.eclipse.tycho.core.UnknownEnvironmentException
at org.eclipse.tycho.core.utils.ExecutionEnvironmentUtils.getExecutionEnvironment(ExecutionEnvironmentUtils.java:87)
at org.eclipse.tycho.core.osgitools.OsgiManifest.parseExecutionEnvironments(OsgiManifest.java:61)
... 25 more
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/InternalErrorException