Here a few things you could try (one after the other):
• Try deleting the preferences file:
1. Quit iWeb
2. Delete the following file:
User/Library/Preferences/com.apple.iweb.plist
3. Relaunch iWeb
If that doesn’t work... Retry it but instead of relaunching iWeb in 3. restart the computer and relaunch iWeb
• Try repairing disk permissions:
1. Go to Applications/Utilities
2. Open Disk Utility
3. Click Macintosh HD
4. Click on Verify Disk Permissions
5. Click Repair Disk Permissions.
• Try with a new Domain file
1. Close iWeb
2.
Click here and a download will start
3. Unzip the file and you will find a file called Domain or Domain.sites2
4. Double-click it and it will open iWeb
5. Hopefully now it will work again and you can start rebuilding your site as of Chapter 2.3 of the Backup and retrieve FAQ on my website.
Regards,
Cédric