Mac App Store: Sign in sheet does not appear, or does not accept typed text
When you attempt to sign in to the Mac App Store, the "Sign in to download from the App Store" sheet may not appear
Even if the sign in sheet is visible, text you type may not appear in the Apple ID or password fields
Third-party software that alters your system, such as FruitMenu or APE (Application Enhancer), may cause these issues.
Disable or remove the third-party software.
If the issue persists after removing the third-party software, reinstall Mac OS X v10.6 from your original install media, followed by installing all updates available from Software Updates.
Important: Information about products not manufactured by Apple is provided for information purposes only and does not constitute Apple’s recommendation or endorsement. Please contact the vendor for additional information.