I am guessing that you are using the copy/paste method to assemble your objects. Bryce seems to get fussy (well, at least for me) when you have a lot of information on the clipboard. Make your separate files, and use the "Merge" command from the File menu to assemble your objects. If you absolutely must use the clipboard for a lot of objects, purge it immediately after pasting by copying something small (like a few letters of text or something.)