When I open an illustrator 10.2 document with illustrator CS5 and then save the new document there is a warning that the new document is 72 ppi or less. If I copy and paste the old drawing onto a new illustrator CS5 file it behaves normally. It seems very inefficient to go through years of drawings and copy and paste all the layers into new documents but I guess if that's the only way I will just gradually do it.
Thanks
Change the Document Raster Effects Settings in the documents as you open them...
Effects > Document Raster Effects Setting
There's no need to copy to a new document. You simply need to correct the setting.