Xcode4 Linking Problem. File was built for archive which is not the architecture being linked (arm6)

Question

Recently, I switched to Xcode4 and when I compile my project I got following error.

ld: warning: ignoring file /Users/myname/Library/Developer/Xcode/DerivedD         


        

Answer 1

I had this problem with the Three20 library. The thing that finally did it for me was switching the Project Format from Xcode 3.1 to Xcode 3.2 - leaving 'build active arch only' as "no".