I ran across a new variation of this problem yesterday. Instead of the
usual problem that shows up from the execute package task, this error
showed up from a data pump in an outer package when executing an
individual data pump task within a package open in DTS Designer. I was
able to fix it by disabling all the tasks that I did not want to run
and running the data pump by executing the whole package. I then
re-enabled the other tasks, saved the package and the problem seemed
to go away and stay away.

Although I have not tried it, this might help with the same problem
popping up from inner packages called from execute package tasks.
Execute the inner package from dts designer and re-save it, then see
if it runs from the outer package. My experience seemed to indicate
previously that this error was also somehow associated with data pumps
in the inner package.

Just thought I would throw this out as another piece of the puzzle,
and another possible solution. Since MS seems unable to fix the
problem maybe we can hope that it will serendipitously disappear with
the next version of DTS which is supposed to be completely reworked.

JP