I too am receiving a similiar error on a couple of my dts schedules out of 1,000.
When I restart the agent service the errors go away for a few days.
Executed as user: TPOWER\TMERADSQL. DTSRun: Cannot create COM Server to load and execute DTS Package. Error -2147221008 (800401F0): CoInitialize has not been called. Process Exit Code -2147221008. The step failed.
Something is leaking somewhere, I'm thinking maybe memory or com handles, I'm not too sure.
Either way, I think its something that MS should have fixed, considering we're now on SP3a.
I'm running Windows Server 2003, and this server only runs dts jobs.
Is it possible that had you not changed the security for the agent and restarted the service it could have worked from restarting the service?
I will try and change the agents login on mine and I'll let you know how I get on.
Anybody else got any possible working solutions?