Attempting to deploy my app on my jailbroken iphone, but the app closes immediately!

I had the same issue, ldid did not work for me at all. Here's my solution:

1. Open Keychain Access on the Mac
2. In the menu, go to "Keychain Access -> Certificate Assistant -> Create a Certification"
3. Name it "Cydia Developer" or whatever, type is "self-signed root" and check "let me override defaults".
4. The only option you need to set in the wizard is to change Certificate Type to "Code Signing". Click continue or enter your desired info for the rest.
5. Once it's created, find it in Keychain Access's Certificates list and right click -> Get Info, under Trust change "When Using This Cert" to "Always Trust".
6. Write an iPhone app in XCode. Change "Project->Project Settings->Build->Code Signing Ident->Any iPhone Device" to "Don't Code Sign".
7. Compile the program with the Active SDK set for "iPhone Device" instead of "Simulator". Ignore the errors about provisioning or signing.
8. Under "Executables", drag the newly compiled app to somewhere that is easy to get to from the terminal.
9. In a terminal, run 'codesign -fs "Cydia Developer" /path/appname.app/appname'
10. Somehow get your app to the phone (ssh, cydia, teleportation, whatever) and viola! Working app.

To deploy with an Apple devel key, just set your project build code sign identity to the name of the Apple dev key name instead of "Don't code sign".

Did you sign your app? I'm not sure if this is needed for Xcode apps, but to run Jailbreak-toolchain compiled apps you have to run ldid -S (as root) on the app executable (ex. MyApp.app/MyApp). This Thread may help: Thread