diff --git a/lib/docker_client.rb b/lib/docker_client.rb
index 5677c047..f6ab6b89 100644
--- a/lib/docker_client.rb
+++ b/lib/docker_client.rb
@@ -26,7 +26,12 @@ class DockerClient
 
     local_workspace_path = local_workspace_path(container)
     if local_workspace_path &&  Pathname.new(local_workspace_path).exist?
-      Pathname.new(local_workspace_path).children.each{ |p| p.rmtree}
+      Pathname.new(local_workspace_path).children.each do |p|
+        p.rmtree
+      rescue Errno::ENOENT => error
+        Raven.capture_exception(error)
+        Rails.logger.error('clean_container_workspace: Got Errno::ENOENT: ' + error.to_s)
+      end
       #FileUtils.rmdir(Pathname.new(local_workspace_path))
     end
   end
@@ -197,12 +202,17 @@ class DockerClient
     container.stop.kill
     container.port_bindings.values.each { |port| PortPool.release(port) }
     clean_container_workspace(container)
+
+    # Checks only if container assignment is not nil and not whether the container itself is still present.
     if container
       container.delete(force: true, v: true)
     end
   rescue Docker::Error::NotFoundError => error
     Rails.logger.error('destroy_container: Rescued from Docker::Error::NotFoundError: ' + error.to_s)
     Rails.logger.error('No further actions are done concerning that.')
+  rescue Docker::Error::ConflictError => error
+    Rails.logger.error('destroy_container: Rescued from Docker::Error::ConflictError: ' + error.to_s)
+    Rails.logger.error('No further actions are done concerning that.')
   end
 
   #currently only used to check if containers have been started correctly, or other internal checks
@@ -400,6 +410,7 @@ class DockerClient
     begin
       clean_container_workspace(container)
     rescue Docker::Error::NotFoundError => error
+      # FIXME: Create new container?
       Rails.logger.info('return_container: Rescued from Docker::Error::NotFoundError: ' + error.to_s)
       Rails.logger.info('Nothing is done here additionally. The container will be exchanged upon its next retrieval.')
     end
diff --git a/lib/docker_container_pool.rb b/lib/docker_container_pool.rb
index 64cd847c..79aeea40 100644
--- a/lib/docker_container_pool.rb
+++ b/lib/docker_container_pool.rb
@@ -52,13 +52,13 @@ class DockerContainerPool
   def self.create_container(execution_environment)
     Rails.logger.info('trying to create container for execution environment: ' + execution_environment.to_s)
     container = DockerClient.create_container(execution_environment)
-    container.status = 'available'
+    container.status = 'available' # FIXME: String vs Symbol usage?
     #Rails.logger.debug('created container ' + container.to_s + ' for execution environment ' + execution_environment.to_s)
     container
   end
 
   def self.return_container(container, execution_environment)
-    container.status = 'available'
+    container.status = 'available' # FIXME: String vs Symbol usage?
     if(@containers[execution_environment.id] && !@containers[execution_environment.id].include?(container))
       @containers[execution_environment.id].push(container)
     else