Files such as .app, .nib, and .mbox are greyed out in the file signature creation dialog box. Most likely, this type of file is a package. File packages are in MacOS 9 and X. They are basically a folder with files that appears as a single file to the user. Because it is not a single file with a single file type, VirtualLab has no way of searching for such a file. You will not be able to use the Undelete function for these types of files.