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Exchange 2019 Setup Prerequisite Check fails for .NET 4.8 Framework in CU4 on Windows builds 1909 and 1903

Symptoms

When you deploy or upgrade to Microsoft Exchange 2019 Cumulative Update 4 (CU4) on Microsoft Windows Server 2019 or Windows 10 (Management Tools only) builds 1909 or 1903, the system prerequisites check fails, and you receive the following error message:

“This computer requires .NET Framework 4.8 (https://support.microsoft.com/kb/4503548).”

By default, Windows builds 1909 and 1903 already have .NET Framework 4.8 installed. When you try to reinstall the software, the installation fails.

Cause

This problem is caused by a prerequisite check that was introduced in Cumulative Update 4. This process checks incorrectly for .NET Framework 4.8. Because the prerequisite check doesn’t recognize that .NET Framework 4.8 is already installed.

Status

Microsoft is researching this problem and will post more information in this article when it becomes available.

Workaround

Important

Follow the steps in this section carefully. Serious problems might occur if you modify the registry incorrectly. Before you modify it, back up the registry for restoration in case problems occur.

  • Start “regedit.exe” as an administrator.
  • Locate the following registry subkey:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full

  • Right-click the subkey, and select Permissions from the shortcut menu.
  • Select Advanced.
  • In the Advanced Security Settings window, locate the Owner attribute at the top of the window.
  • Select Change next to the listed owner.
  • In the Enter the object name to select field, enter the name of the local administrator group. For example, enter <computername>\Administrator. Then, select OK.
  • In the Advanced Security Settings window, select the local administrator group that you changed ownership to, and then select Edit.
  • Change the basic permissions to Full Control.
  • Select OK three times to save the changes and return to the main Registry Editor window.
  • Locate the following key in the path:

Name: Release
Type: REG_DWORD
Data: 528040 (decimal)
Change the Data value to 528049 (decimal)

  • Rerun the Exchange system prerequisites check, and deploy or update Exchange Server 2019.
  • Start Registry Editor, locate the subkey that’s mentioned in step 2, repeat the necessary steps to locate the Release key, and then revert the Data value to 528040 (decimal).

This should allow everything to run correctly after the installation.

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REFERENCES
Exchange CU4 Prerequisite Check Fails for .NET 4.8 for Windows Server builds 1909 and 1903

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