Update to 10.5.3 so your data can be saved.
 

If you're running 10.5 (aka Leopard), you may have encountered a crash when saving a new document, or using "save as" to copy your document. This issue appears to be addressed in Apple's recent update, 10.5.3.

We encourage our 10.5 users to update to 10.5.3, unless of course you like losing your data just when you're ready to save it. Please let us know if you experience crashes while saving (or of any other flavor) on 10.5.3.