Error: ld: 1 duplicate symbol for architecture arm

Question

I have looked everywhere and cannot find the solution to this problem. I have tried renaming the .h/.m files deleting them and creating them again as well as seeing if the problem is with the files not being in the compile sources in the project manager.

This is the error:

Ld /Users/mabdelhamid/Library/Developer/Xcode/DerivedData/Markschemes-dksalheponzwnocllyohgwmotxho/Build/Products/Debug-iphoneos/Markschemes.app/Markschemes normal armv7
cd "/Users/mabdelhamid/Desktop/Application Backup/MarkSchemes 14:08"
setenv IPHONEOS_DEPLOYMENT_TARGET 6.1
setenv PATH "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin:/Applications/Xcode.app/Contents/Developer/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin"
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang -arch armv7 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS6.1.sdk -L/Users/mabdelhamid/Library/Developer/Xcode/DerivedData/Markschemes-dksalheponzwnocllyohgwmotxho/Build/Products/Debug-iphoneos -F/Users/mabdelhamid/Library/Developer/Xcode/DerivedData/Markschemes-dksalheponzwnocllyohgwmotxho/Build/Products/Debug-iphoneos -filelist /Users/mabdelhamid/Library/Developer/Xcode/DerivedData/Markschemes-dksalheponzwnocllyohgwmotxho/Build/Intermediates/Markschemes.build/Debug-iphoneos/Markschemes.build/Objects-normal/armv7/Markschemes.LinkFileList -dead_strip -fobjc-arc -fobjc-link-runtime -miphoneos-version-min=6.1 -framework MessageUI -framework QuartzCore -framework UIKit -framework Foundation -framework CoreGraphics -o /Users/mabdelhamid/Library/Developer/Xcode/DerivedData/Markschemes-dksalheponzwnocllyohgwmotxho/Build/Products/Debug-iphoneos/Markschemes.app/Markschemes

duplicate symbol _penaltyCriteria in:
/Users/mabdelhamid/Library/Developer/Xcode/DerivedData/Markschemes-dksalheponzwnocllyohgwmotxho/Build/Intermediates/Markschemes.build/Debug-iphoneos/Markschemes.build/Objects-normal/armv7/MHTFrontViewController.o
/Users/mabdelhamid/Library/Developer/Xcode/DerivedData/Markschemes-dksalheponzwnocllyohgwmotxho/Build/Intermediates/Markschemes.build/Debug-iphoneos/Markschemes.build/Objects-normal/armv7/MedIFrontViewController.o
ld: 1 duplicate symbol for architecture armv7
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Please someone help me figure this out.

If I select either .m file and uncheck the target membership from the file inspector in the utilities area the error disappears but my class is then unusable.