Working with sub projects in a master project file

[sergio espinosa]

I am in the process of compiling a master project file
with several sub-projects listed as tasks. I have linked
each one correctly however when I go back to expand the
task list on one project I am getting the follwoing
error...."A project can be inserted only once in a
consolidated project. Select a different project to
start." I am not trying to insert it again - I just want
to go in and update it. Any ideas what I can do to avoide
this error and allow the update? Thanks, Sergio