A family of Microsoft relational database management systems designed for ease of use.
Chris,
You're welcome. The error message is something I might expect to see if there were an issue with a fixed cost entry. You mentioned you were completely sure whether the subproject files had cost or resources assigned. It should be pretty obvious. Open each subproject and display the Cost field and Resource Names field. While you at it you might also wan to display the Fixed Cost field.
As I mentioned, it's possible one or more of you files is corrupt. Open each subproject and save as XML. Then re-open into Project. Now try to build a new master with those "cleaned" files.
John