What system and iWeb version are you using?
Try the following:
1 - delete the iWeb preference file, com.apple.iWeb.plist, that resides in your
User/Home/Library/ Preferences folder.
2 - delete iWeb's cache file, Cache.db, that is located in your
3 - launch iWeb and try again.
NOTE: In Lion and Mountain Lion the Library folder is now invisible. To make it permanently visible enter the following in the Terminal application window: chflags nohidden ~/Library and hit the Enter button - 10.7: Un-hide the User Library folder.
If that doesn't help continue with:
- move the domain file from your Home/Library/Application Support/iWeb folder to the Desktop.
- launch iWeb, create a new test site, save the new domain file and close iWeb.
- go to the your Home/Library/Application Support/iWeb folder and delete the new domain file.
- move your original domain file from the Desktop to the iWeb folder.
- launch iWeb and try again.
If you're running Lion or Mt. Lion read the following;
To open your domain file in Lion or Mountain Lion or to switch between multiple domain files Cyclosaurus has provided us with the following script that you can make into an Applescript application with Script Editor. Open Script Editor, copy and paste the script below into Script Editor's window and save as an application.
do shell script "/usr/bin/defaults write com.apple.iWeb iWebDefaultsDocumentPath -boolean no"
tell application "iWeb" to activate
You can download an already compiled version with this link: iWeb Switch Domain.
Just launch the application, find and select the domain file in your Home/Library/Application Support/iWeb folder that you want to open and it will open with iWeb. It modifies the iWeb preference file each time it's launched so one can switch between domain files.
WARNING: iWeb Switch Domain will overwrite an existing Domain.sites2 file if you select to create a new domain in the same folder. So rename your domain files once they've been created to something other than the default name.