Then, your project file might be corrupted I guess.

Usually in full versions of IS that value the error is reporting belongs to an specific entry, try the following :

1.open your ism project
2.Click on plus sign to open "Organize your setup option" branch
3.In "General Information", look for "Published/Product URL" entry and type something, your own url or any other one.
4.Rebuild your project

Tell me if you owe me a beer. ;)