There's a bug in the app, which prevents more than 1 task starting simultaneously. To do this you should create / modify your app_config.xml file in the projects\www.gpugrid.net folder.

<app_config>
  <app>
    <name>QC</name>
    <max_concurrent>1</max_concurrent>
  </app>
  <app_version>
    <app_name>QC</app_name>
    <plan_class>mt</plan_class>
    <avg_ncpus>4</avg_ncpus>
  </app_version>
</app_config>

Have you ever tried using???

<fetch_minimal_work>1</fetch_minimal_work>

Fetch one job per device (see --fetch_minimal_work).

--fetch_minimal_work

Fetch only 1 job per device (CPU, GPU).
Used with --exit_when_idle, the client will process one job per device, then exit. [/code]