Putting a new XIB file in my project gives problems with "keys"

I'm trying to make a menu for my app which I already made. I added a new .m-file, .h-file & a nib file and named this Menu. Within my P-list i have set Menu as "Main nib file base name (iPad)".

When I run this project I get this error:

"Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[ setValue:forUndefinedKey:]:开发者_JAVA技巧 this class is not key value coding-compliant for the key opstelling."

Any suggestions how I can fix this error?

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Check your class instance (or reference if it is the file's owner) in your nib file by right-clicking it and see if there is no key "opstelling" being used there