I had the same problem when I switched to new iMac w/OS10. None of my OS9 documents would open w/o a great deal off futzing around. Amos came up with an elegant solution....I just have to rename the file with convention used by current WP. I.E., rename What is Art (old fild name) What is Ark.cwk (new convention). When I do this a window appears asking me if I want to rename the file. I click yes, then when I open, another window tells me file has been renamed....and it opens just fine.

Have no idea if WP stuff might work the same but it's easy to try, anyway.