Jenkins/Maven build dying with "Could not find the selected project in the reactor" error
Take a look at what Maven is executing:
Executing Maven: -B -f /scratch/jenkins/workspace/subco/subco/pom.xml -amd -pl org.mainco.subco:oldmodule,org.mainco.subco:subco,org.mainco.subco:moduleB,org.mainco.subco:database,org.mainco.subco:moduleF,org.mainco.subco:moduleA,org.mainco.subco:moduleH,org.mainco.subco:newmodule,org.mainco.subco:session,org.mainco.subco:moduleA,org.mainco.subco:newmodule,org.mainco.subco:moduleB clean install -e -P qa -P cloudbees -DskipITsIn the -pl part is your old module. As you tell maven to use the parent project to build a module that's no longer part of that project, it fails.
Where is that command generated? Is suspect the old module be in one of your maven profiles or the Jenkins configuration.