Fix "Source Files could not be Found or Downloaded" in
Windows 8 and Later
Windows 8, 8.1, Server 2012 and 2012
R2 come with only .NET
Framework 4.5 fully installed. However, some apps such as CTI Navigator
Desktop require that some components of an earlier version of .NET Framework (such as
3.5, 3.0 or 2.0) also
be installed in order to run properly. Normally, if an app needs a .NET
Framework feature that is not already installed, Windows will automatically
prompt you to install the missing Windows feature over the Internet. If so prompted, select "Install this
Otherwise, you can manually enable .NET Framework 3.5
(which includes code from earlier versions) as follows.
To enable the .NET
Framework 3.5 in Control Panel
- In Windows 8.1: Right-click on the
Start icon and select Control Panel.
In Windows 8: On the
Start screen, type and then choose
Control Panel. (To
access the Start
screen, press the Windows logo key on your
- Choose Programs
(or Programs and Features),
and then choose Turn
Windows features on or off.
- Select the .NET
Framework 3.5 (includes .NET 2.0 and
3.0) check box so the box displays a
that only part of the feature is enabled).
Note: The two “Windows Communication Foundation
sub-features in .NET Foundation 3.5 do not
need to be activated.
- Click OK.
Some Windows security updates
(such as KB2966826, KB2966827, and KB2966828)
can interfere with installing earlier versions of .NET
Framework. This can result in error messages such as
- 0x800f0906: "The
source files could not be downloaded..."; or
- 0x800F081F: "The source files
could not be found...).
A "Fix it
" file can be downloaded
from the Microsoft Download Center to resolve such
errors. Select the package appropriate for your
operating system type: 32-bit or 64-bit. (System Type is
indicated under System in the Windows Control
for details regarding this problem.