Earlier I was trying to add a network exception in iOS. I was advised to do so in info.plist. While doing that, I found the main entry 'Information Property List'. It was collapsed. I did a right click, and then add new row.
At this point, the whole Key with all its fields went black and all the iOS settings were also set to blank. Now, when I run the app, it comes back and says 'Installation Failed' invalid argument with a big blue button for OK.
Step 1: Open the plist file as "source code". See if the original data is there, but with an extra / duplicate entry that's causing it to be invalid.
Step 2: Create a new project, using the same name and initial parameters as your existing project... Copy the resulting plist file from new project to old project.
Step 3: Change the curriculum of your training to include keeping copies / making backups / using source control (this maybe should be Step 1).