I get this same error in Project 2003 and Project Server, however it is not an authentication problem.
The error is related to (I believe) a duplicate record in the web assignments table. You can create this error in either of two ways:
1)
Create a project with a task.
Build a team that includes a resource (it can be you - I used myself in this example)
Assign yourself to the task
Save the project to the server, but do not publish it
Now go to your tasks and "Assign myself to an existing task".
Select the project and task that you just created
enter some time and update the task
Now, when you go back into MSP and try and publish the project, you will get the spooler error since you (the resource) have two assignments on the same task - the assignment you created in Project as the Project Manager and the assignment you created in tasks as the resource on the project.
2)
I can also cause this same error by hiding a task in my timesheet and then re-adding it (as above). This situation is even more problematic as the hidden task may have actuals in the project.
So here are my questions:
1) How does one get rid of these conflecting assignments so the project can again be published?
2) How do we keep these problems from re-occuring?
This is turning into a HUGE issue!