The problem has turned out to be a permissions issue. The disabled processes were not enabled to the general group of developers. There is a LDAP group as Developer and the processes were allowed to be executed by this general group. Particular for this project, this privilege was not defined for the general group. The user was also not among the LDAP groups which have the rights to execute the processes. I have added the general group Developer to the Access list and the issue has been resolved.