Installing Microsoft .NET Framework 4.0 failed (5100)

Summary: How to fix the Installation Error 5100.
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Problem

According to Microsoft, the 5100 return code is related to system requirements.

Solution 1

Reboot the computer.

If the previous setup required a reboot, it may not have finished. After this reboot, the .NET Framework 4 setup should be installed.

Solution 2

Does the target system have enough hard disk free space? The .NET 4.0 minimum requirement is 2 GB disk space for installation. Free up space in the installation drive and installing it will work fine.