+1  A: 

You must re-install Xcode using the version on the Snow Leopard DVD. The iPhone SDK must be re-installed afterwards.

Edit: I just noticed that Apple started distributing Xcode 3.2 with the iPhone 3.1 SDK. I would recommend you to attempt a full uninstall of the developer tools, as described in the SDK release notes (see developer.apple.com), and then to re-install it. You should also check that each computer have a unique name set in system preferences>>sharing. As a last resort, I'd check that Snow Leopard was booted in 32-bit mode (it does by default), and (just for the test) try to boot Snow Leopard in 64-bit mode (hold the 6 and 4 keys while booting).

Edit 2: Check this thread, it seems related. Maybe you should try to enable Xgrid in sharing preferences?

Ludvig A Norin
Some MacBooks cannot boot in x64 mode (disabled by Apple). Also Xgrid enablement does not solve this problem.
Sorin Sbarnea
+2  A: 

The solution seems to be to run Xcode in "32-bit" mode - you set this in the "Get Info" dialog in the Finder.

Bids
A: 

I had a problem installing it now it works since it needed for the xcode and ipphone sdk the firewall disabled to install, I think that fix my problem where it did not want to install the files strange bug I guess, with firewall on , the installer fails to install, and I am still in 64bit mode

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