XCode can't be installed because the version of OS X is "too new"

I have Mountain Lion installed on both my iMac and my MacBook, and I'm trying to install XCode from the App Store. It installed on the MacBook without an issue, but when I try to install it on the iMac, I get an error that says "XCode can't be installed because the version of OS X is too new". Is there anything I can do about this? I'm running Mac OS X 10.8.0.

Thanks in advance 🙂