The VDA Agent Software installation fails to initialize the component and pop-up with the error:
"The Program can't start because mfc120u.dll is missing from your computer. Try reinstalling the program to fix the problem."

OR
While you are able to get past the installation. Then the VDA launch for ICA session would bring up the following error:
"There was a problem starting C:\Program Files\Citrix\ICAService\CtxLocationApi64.dll. The Specified module could not be found"

Note: The issue only happens when we have a partial or no install of "Microsoft Visual x64 C++ 2013 / 2015 Runtime".

Caution! Using Registry Editor incorrectly can cause serious problems that might require you to reinstall your operating system. Citrix cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk. Be sure to back up the registry before you edit it.

The 7.1x VDA Agent software requires both variants "Minimum" and "Additional" of the Runtime VC++ library to function. So fix this you may try any of the following measures:

• Install the VC++ Runtime Libabry by browsing the Product ISO folder (Drive:\Support\<VCredistXXXX>).
• Uninstall the said application from the VDA (Desktop / Server). And install the VDA Agent software first followed by the Application. This is also Citrix recommended best practices. 
• Review the bug# LC9979 for updates or Private fixes and instructions. The bug addresses the need of our meta-installer to validate any missing variant and provide next possible steps.

Review the MSI Log file for the VC++Runtime and the XenDesktop VDA Agent installation file for more details. This will also provide the GUID of the Runtime install.

NOTE: The Bug# LC9979 to be referred for more details. This fix has been released to public in CU3 of the LTSR 7.15 branch for both x86 and x64 architecture.

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Problem Cause

The MFC files are NOT available in the "Minimum" variant of the Runtime Installation.

A little background on why this issue happens.

Microsoft allows software vendors to install Microsoft VC++ (x86 / x64) Runtime libraries in either "Minimum" And / OR  "Additional" variants for same version. Or you can say permits parallel install of both variants.
This can be checked under "Programs and Features or Appwiz.cpl".

Note: The application vendors can also HIDE these Runtime Libarary installs by passing a argument during install, which can be checked in the Windows Registry at the following location:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\
One has to explore the random generated GUID under this Key and look for the "DisplayName".

The Parameter "SystemComponent" with REG_DWORD 0x0 allows it to be hidden and not visible in the Programs and Features control panel applet. You can unhide by flipping the DWORD to 0x1.

https://support.microsoft.com/bn-bd/help/2977003/the-latest-supported-visual-c-downloads
https://www.citrix.com/downloads/citrix-virtual-apps-and-desktops/product-software/xenapp-and-xendesktop-715-ltsr-cu3-all-editions.html