Mac OS X wants to use system keychain when compiling the project

1. Open Keychain Access.
2. In the top-left corner, unlock the keychain (if it is locked).
3. Choose the System keychain from the top-left corner.
4. Find your distribution certificate and click the disclosure triangle.
5. Double-click ‘Private key’ under your distribution certificate.
6. In the popup, go to the Access Control tab.
7. Select ‘Allow all applications to access this item’.
8. Save the changes.
9. Close all windows.
10. Run the application.

The problem is with the Developer Certificate on Keychain which is under "System", on the left hand panel, which is always locked and requiring my password to unlock!

So just move the Developer Certificate to "login", which is always unlocked. Now your problem gets solved.

1. Open Keychain Access

2. Click on System in left pane

3. Unlock the System keychain top left (if it is locked)

4. Sort the System items by Kind so that the keys are at the top

5. Look for the private key that keeps asking for password

6. Double click on it and choose Access Control

7. Choose "Allow all applications to access this item"

8. Save changes, lock the System keychain and quit the Keychain app

9. Restart the application that keeps asking to modify your keychain

I was getting this problem because I had duplicate certificates in my login and System keychains. By opening Keychain Access and deleting all certificates from System that were also in login solved this problem. Hope this helps.