When jdk/jre installation is accepted it doesn't check that the same version has been already installed.

Steps:

1. Launch jdk/jre installation and leave it in pre-accepted state
2. Launch second jdk/jre installation, accept it and install
3. Accept firstly launched installation, the next error will occur

In case of jdk installation:
Error 1721 - There is a problem with Windows Installer package. A program required for this install to complete could not be run. Contac your support personnel or package vendor.
In case of jre installation:
Error 1316 - A network error occurred while attempting to read from the file C:\Documents and Settings\Administrator\Application Data\Sun\Java\jre1.6.0_12\jre1.6.0_12.msi