Back up the registry.

Start Registry Editor. To do this, click Start, click Run, type regedit, and then click OK.

Locate and then click to select the following registry sub key:

HKEY_LOCAL_MACHINE/Software/Microsoft/NET Framework Setup/NDP

After you select the subkey that is specified in step 3, point to New on the Edit menu, and then click Key.

Type WU, and then press ENTER.

Right-click WU, point to New, and then click DWORD Value.

Type BlockNetFramework451, and then press ENTER.

Right-click BlockNetFramework451, and then click Modify.

In the Value data box, type 1, and then click OK.

On the File menu, click Exit to exit Registry Editor.