I have been working for a while to create an iPhone app. Today when my battery was low, I was working and constantly saving my source files then the power went out...
<change your current project folder nam and checkout module the same project.then add the current file changes.
And once you get things working again you should look into using something like subversion or mercurial for backup and revision control. Remember that he electrons don't always go where they are supposed to, backup early and often!
Just check the project.pbproject file and do a diff against a working version of the project file.
Often times this happens when you have conflicts from a version control system like posted here: User file cannot be parsed in subversion in MAC iphone SDK