"The application has failed to start because its side-by-side configuration is incorrect"

This message is about older Windows programs. “Side-by-side” is Microsoft’s system for keeping several versions of the Visual C++ runtime installed at once. The program asked for a specific version — most often the 2005 or 2008 set — and that version isn’t on this PC, or its registration is damaged.

The fix, in order

  1. Install the Visual C++ 2005 Redistributable (SP1) from Microsoft, both x86 and x64 — this is the version older programs ask for most.
  2. Add the 2008 and 2010 Redistributables the same way (SP1 builds, both flavours). Each is small, and having the set covers nearly every program that raises this message.
  3. Restart and try the program again. Most cases end here.
  4. If it persists, repair Windows’ component store: admin Command Prompt → sfc /scannow, then DISM /Online /Cleanup-Image /RestoreHealth.
  5. For a precise answer, run sxstrace: it logs exactly which runtime version the program requested (see “Still happening” below), so you install that one instead of guessing.

If it still happens

To find the exact missing piece: open Event Viewer → Windows Logs → Application and look for a “SideBySide” error at the time you launched the program — it names the runtime version requested. Or run `sxstrace trace -logfile:sxs.etl` from an admin prompt, launch the program, stop the trace, and convert it with `sxstrace parse`. Either way, install the version it names.

Common questions

Which redistributable do I actually need? For this message, most often the 2005 SP1 set, then 2008 SP1. Installing 2005, 2008 and 2010 in both flavours covers the overwhelming majority of programs — it takes a few minutes and they don’t conflict.

Did I break something to cause this? No. The runtime was likely never installed on this PC, or a Windows reinstall/upgrade left it behind. The program itself is usually fine.

Related errors

MSVCP140.dll missing · Error 0xc000007b — unable to start correctly · Visual C++ Runtime Library error