Fix An error occurred while saving the URL rewrite, quick and easy fix for this problem.
We always recommend making FULL site backups before commencing.
This error normally shows up on a Magento 1.4x installation, the fix we found was to simply to re-index the site:
Admin -> System -> Index Management -> Select All and Reindex
If this doesn’t fix your problem, then try one (or all) of the following
1. Change the permissions of your media folder to 777.
2. Flush your cache, by deleting the /var/cache/ directory *
3. Delete your sessions, by removing your /var/sessions folder *
4. Try replacing your root .htaccess file with a default .htaccess file suitable for your Magento version