Helloword developed by ADT cannot be installed on happy phone

Development Environment: windows7 + jdk1.6 + eclipse3.7 + ADT + Android SDK 2.2
Running Environment: Happy phone + happy os2.0 (andorid2.2)
Performance problem: the system prompts that helloword cannot be installed on this mobile phone.
Problem Analysis:
1. Make sure that the development version is consistent with the running version;
2. Whether or not the APK is generated using the signature method;
Signature function:
1. Use a special key signature to obtain different permissions.
2. if an APK uses a key signature, the file with the other key signature cannot be installed or overwrite the old version at the time of release, which can prevent your installed application from being overwritten or replaced by malicious third parties.