If you are getting “side-by-side configuration is incorrect. Please see the application event log or use the command-line sxstrace.exe tool” error when you try to start apache, you most likely need to install Microsoft Visual C++ Redistributable as PHP might be compiled using it. You can find links to VC redistributable below.

Detailed Explanation:
I installed xampp on a new windows 2008 server. Installation was successful. I did not see any errors while I was installing it. I opened xampp control panel to look at the apache, mysql services to see if they are running. I noticed apache service was not running. i tried to start apache manually by clicking start button in xampp control panel. It did not start. But other services like mysql, filezilla were running fine without any problem.

I opened cmd prompt and went into c:\xampp folder & tried to start apache by typing apache_start. I got below error in the cmd prompt

The application has failed to start because its side-by-side configuration is incorrect. Please see the application event log or use the command-line sxstrace.exe tool for more detail.

I found below error in windows event viewer log

Activation context generation failed for “C:\xampp\apache\bin\httpd.exe”. Dependent Assembly Microsoft.VC90.CRT,processorArchitecture=”x86″,publicKeyToken=”1fc8b3b9a1e18e3b”,type=”win32″,version=”9.0.21022.8″ could not be found. Please use sxstrace.exe for detailed diagnosis.

It said something about microsoft VC9. I tried to find what version they used to compile it. I found it in readme_en.txt under c:\xampp. PHP was complied in VC9 X86 32bit thread safe.

As server was missing runtime components of Microsoft Visual C++ (VC9), It gave that error. It can be fixed by installing Visual C++ redistributable package.

If your server is 32 bit, Install Microsoft Visual C++ 2008 Redistributable Package (x86)

If your server is 64 bit, install both x86 version (above link) & Microsoft Visual C++ 2008 Redistributable Package (x64)

This should solve this problem.