.) Informatica power center jobs not starting after agent ended in ended_lost status.
.) Jobs remain stuck in status "Active".
.) The Automation Engine was from Servicepack 8 and the Ra-Core from Servicepack 3
These components are not compatible therefore the Server was not able to receive status messages from the agent anymore.
The following Steps solved the Problem:
1) End the Agent
2) Remove all restart files from the BIN Folder
3) Manually End all Active Informatica Jobs running on this Agent.
4) Upgrade the RA Core to a compatible version
5) Erace all files from the Temp folder of the Agent
6) Start the Agent.