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After you install and start Microsoft Virtual PC 2004 Service Pack 1 (SP1), you receive the following error message:
Missing or Invalid Product Key.
This problem occurs if you perform a quiet (unattended) installation of Virtual PC 2004 SP1 by using the following command line: msiexec.exe /i "Drive_letter:\Path\Microsoft Virtual PC 2004.msi" /qn.
A typical installation of Virtual PC 2004 SP1 uses the Setup Wizard. A typical installation saves the product key for Virtual PC 2004 for use with Virtual PC 2004 SP1. When you perform a quiet installation, the product key is not saved correctly. Therefore, the error occurs.
To work around this problem, you can perform a quiet installation of Virtual PC 2004 SP1 by using the PIDKEY Setup switch, as in the following example: msiexec.exe /i "Drive_letter:\Path\Microsoft Virtual PC 2004.msi" /qn PIDKEY=XXXXXXXXXXXXXXXXXXXXXXXXX, where the string of "X" characters is your 25-character Product Identification number for Virtual PC 2004 SP1.