OS X app on Lion 10.7.2 Xcode 4.3 :: error: failed to launch <exe path> -- SBTarget is invalid

This happened to me, and the issue I had was the schema Target was correct but 64 bit was selected in as the architecture instead of 32 bit, for a 32 bit only project. Once I made the switch, it started working again.

GDB had the same issue but did not report it so elegantly, instead it reported "warning: posix_spawn failed, trying execvp, error: 86". It did launch the app but could not debug it.

This can easily happen if you debug without building the project, after switching the schema, or if the schema gets switched for you due to an external change to the project file (updating or reverting your source repository using git, svn, ...)

I tried everything metioned here. Nothing worked. It seems that I somehow imported the Info.plist twice. To fix it I selected the project and pressed the "Validate Settings" button. Afterwards it works for me.