Xcode has no rule to process .xib files in one of my projects

FROM : Arne Scheffler
DATE : Sat Feb 23 09:38:28 2008

Hi,
I have one project where I added a .xib file and Xcode sees it as 
"sourcecode.xib" filetype. When I build this project I get the 
following output from the compiler:

warning: no rule to process file '$(PROJECT_DIR)/../../frame/resource/
menubar.xib' of type sourcecode.xib for architecture i386

This project has a long history and was first created with Xcode 2.0. 
When I add the .xib file to another project I get this output:

CompileXIB /Volumes/bla/frametst/mac/../../frame/resource/menubar.xib
    cd /Volumes/bla/frametst/mac
    /Developer/usr/bin/ibtool --errors --warnings --notices --output-
format human-readable-text --compile /Volumes/bla/frametst/mac/build/
Debug/frametst.app/Contents/Resources/menubar.nib /Volumes/bla/
frametst/mac/../../frame/resource/menubar.xib
/* com.apple.ibtool.document.notices */
/* com.apple.ibtool.document.warnings */
/* com.apple.ibtool.document.errors */

The rules section of the targets in both projects are identical.
Any hints on how to fix this ?

arne