Apple has started requiring that all code on the device is signed. This is mostly to make it impossible for programs running through Apple's AppStore to download more software and run it.
Three options are available for you!
Self-Signing
Simple method. Using Apple's codesign tool to sign the binary.
mac$ platform=/Developer/Platforms/iPhoneOS.platform
mac$ allocate=${platform}/Developer/usr/bin/codesign_allocate
mac$ export CODESIGN_ALLOCATE=${allocate}
mac$ codesign -fs "Name" Program
Pseudo-Signing
Install using Cydia or APT.
iphone# apt-get install ldid
iphone$ ldid -S Program
Disabling Checks
sysctl -w security.mac.proc_enforce=0
sysctl -w security.mac.vnode_enforce=0
If you start noticing problems all you got to do is change the variables.
sysctl -w security.mac.proc_enforce=1
sysctl -w security.mac.vnode_enforce=1