How do I fix the side-by-side configuration error in FSX?

The “side-by-side configuration is incorrect” error in Microsoft Flight Simulator X (FSX) or FSX: Steam Edition means Windows cannot load an assembly required by the simulator or an add-on—usually an x86 Visual C++ runtime, sometimes legacy SimConnect. Find the matching SideBySide event, then repair the exact component it names.

What does “side-by-side configuration is incorrect” mean?

Windows is failing to build the activation context that tells an executable which shared components to load. Side-by-side assemblies allow several Visual C++ and SimConnect versions to coexist, so installing the newest package does not automatically replace an older one.

This is the same error shown as “configuration côte à côte incorrecte” on French Windows. Whatever the Windows language, it is a dependency error—not an FSX graphics setting, monitor configuration or aircraft configuration problem.

The executable named in the event matters. If the path ends in fsx.exe, investigate FSX and its prerequisites. If it names a weather engine, traffic utility, launcher, installer or other add-on, repair that programme’s dependency rather than reinstalling the whole simulator.

How do I find what is missing?

The matching SideBySide entry in Event Viewer usually identifies what is missing and which executable requested it.

1. Reproduce the failure once. Note the time and whether you opened FSX itself or a separate add-on.
2. Open Event Viewer. Press Windows+R, enter eventvwr.msc, then open Windows Logs > Application.
3. Find the matching SideBySide event. Check entries at the failure time. The message may say “Activation context generation failed” and show the executable path, dependent assembly and processor architecture.
4. Confirm the failing executable. Do not assume every SideBySide event belongs to FSX; Windows may have recorded an unrelated programme at nearly the same time.
5. Use sxstrace if the event is vague. Open Command Prompt as administrator and run sxstrace Trace -logfile:%TEMP%\fsx-sxs.etl. Reproduce the error, return to the prompt and run sxstrace StopTrace, followed by sxstrace Parse -logfile:%TEMP%\fsx-sxs.etl -outfile:%TEMP%\fsx-sxs.txt.
6. Read the first unresolved reference. Open the generated text file and find the first ERROR or “Cannot resolve reference” line. Later errors may simply be consequences of that first missing assembly.

Which Visual C++ redistributable does FSX need?

For fsx.exe, install the x86 runtime identified by the event or trace. FSX is a 32-bit application, so an x64 package alone cannot satisfy its dependency even on 64-bit Windows.

VC80 means the Visual C++ 2005 generation and VC90 means 2008. Other add-on executables may request different generations or architectures, so follow the failing executable’s record rather than installing packages at random.

1. Look for the named redistributable. Open Programs and Features and locate the matching Visual C++ generation and x86 architecture.
2. Use Repair if offered. Rerun the Microsoft-signed redistributable installer and select its repair option. If the package is absent, install it from the trusted prerequisite files supplied with FSX, Steam or the affected add-on.
3. Restart and reproduce the error. Check a fresh SideBySide event. If it now names something different, the first repair worked and another dependency also needs attention.

A mistake we see repeatedly is removing every Visual C++ redistributable before reinstalling one package. These versions are designed to coexist, and deleting them can break other simulators and utilities.

What if the error names SimConnect?

A SimConnect reference means the named executable expects a specific legacy FSX SimConnect assembly that Windows cannot find or load.

Several SimConnect versions can be installed together. Use the version identified by the trace, from the affected add-on’s prerequisite installer or the FSX SDK\Core Utilities Kit\SimConnect SDK\LegacyInterfaces area when that folder is available. Do not copy an arbitrary SimConnect.dll into the FSX or Windows folders.

Our FSX SimConnect diagnosis and repair steps explain how to match the assembly version and handle the bundled installers in FSX: Steam Edition.

How should I repair the FSX installation?

Repair FSX files only when the event identifies fsx.exe, a stock FSX manifest or another file inside the simulator installation.

FSX: Steam Edition

Open the simulator’s Steam properties and use the Installed Files option to verify file integrity, then launch FSX once through Steam. Back up manually edited default files first because verification can restore the original copies.

Verification repairs the game files; it does not necessarily repair a damaged Windows runtime or third-party add-on. If FSX opens afterwards but reports that individual modules cannot be loaded, follow our guidance for identifying damaged FSX files and add-on DLLs.

Boxed FSX

Run Repair using the matching FSX installation media, then restore the appropriate SP1, SP2 or Acceleration installation state. Do not apply boxed-edition service packs to Steam Edition; our boxed FSX service-pack and Acceleration order shows which updates belong together.

If the boxed installer cannot locate FSX or points to an old folder, fix the installation path before attempting another repair. Use our procedure for restoring FSX’s installation-path registry entries; a registry correction is not otherwise a general fix for missing side-by-side assemblies.

What if FSX still gives me this error?

If the error remains, compare a fresh SideBySide event with the original instead of repeating the same repair blindly.

• The event still names the same Visual C++ assembly: check that you installed x86 rather than only x64, used the generation named in the trace and repaired the dependency for the correct executable.
• The event now names another assembly: the first repair succeeded. Repair the newly identified component.
• The path names an add-on executable: reinstall that add-on or its prerequisite package, not FSX.
• The path names a malformed local manifest: remove no files manually; repair the programme that installed the manifest.
• Several unrelated programmes show SideBySide errors: on Windows 10 or 11, run DISM /Online /Cleanup-Image /RestoreHealth from an administrator Command Prompt, followed by sfc /scannow. Restart Windows, then repair the named runtime again.

Will reinstalling Flight Simulator X fix it?

Reinstalling FSX helps only when its own files are damaged. It will not reliably fix a missing Windows runtime, a legacy SimConnect assembly required by an add-on or a malformed manifest belonging to another programme.

Use a full reinstall only after Event Viewer identifies FSX itself and Steam verification or the boxed Repair option has failed. Preserve add-on installers, activation details and manually changed files before removing the simulator.

Which side-by-side fixes should I avoid?

• Do not download loose msvcr, msvcp or SimConnect.dll files and place them in the FSX, System32 or SysWOW64 folders.
• Do not delete assemblies or manifests from WinSxS.
• Do not assume the latest Visual C++ redistributable replaces the older generation named in the event.
• Do not uninstall every Visual C++ package or install every version you can find.
• Do not mix boxed FSX service packs with FSX: Steam Edition.
• Do not rely on compatibility mode or “Run as administrator”; neither supplies a missing assembly.