WAMP shows error 'MSVCR100.dll' is missing when install

The MSVCR100.dll file is part of the Microsoft Visual C++, redistributables. You can install them and see if this solves your problem. After you install the above check if your wamp installation is correctly setup. Search for "my wamp icon stays orange" posts.

UPDATE 2019

Wampserver 3 requires Visual C++ Redistributable for Visual Studio 2012 Update 4 You can download it at: https://www.microsoft.com/en-us/download/details.aspx?id=30679 There you can select the x86 or x64 version depending on your system

This article on the WampServer forums shows all the Microsoft Visual C++ runtime libraries you need to have installed on your system for each version of WampServer. To quote:

For Windows 32 : Be sure that you have installed the Visual C++ 2010 SP1 Redistributable Package x86 : VC10 SP1 vcredist_x86.exe

http://www.microsoft.com/download/en/details.aspx?id=8328

For Windows 64 : Be sure that you have installed the Visual C++ 2010 SP1 Redistributable Package x64 : VC10 SP1 vcredist_x64.exe

http://www.microsoft.com/download/en/details.aspx?id=13523

Apache will not run without this component

In fact if you are running the 64bit Windows it is a good idea to install all the 32bit libraries as well as the 64bit ones. After all 64bit windows runs 64 and 32 bit code. You will probably find you need at least one of the 32bit runtimes for some app/utility you will install at some point.

UPDATE

If you are running WAMPServer 2.5 you also need the VC11 redist. Visual C++ Redistributable for Visual Studio 2012

29.08.2014 with WAMP 2.5 I agree that VC11 is needed and it is not a bad idea to have previous distributions installed. It will be needed by other application. I am not sure if you need bit 32 version

http://www.microsoft.com/en-us/download/confirmation.aspx?id=30679

UPDATE Aug. 3rd 2016

As I was informed by Fred -ii- (many thanks by the way) the link for the post in the wamp forums doesn't work anymore. Since I could not find the original link you can try http://forum.wampserver.com/read.php?2,138295. It has lots of info and may help you.

For me none of the above answers worked so I am adding what worked for me. I first installed the files mentioned in the accepted answer and when that not worked, I downloaded files from this link and it started working.

So I think 2012 distribution is also needed (I am using window7 home basic 64 FYI).

I solved this problem by installing this one : http://www.microsoft.com/en-sg/download/details.aspx?id=30679

Be sure to remove wampserver and reinstall it again

Note: I'm using Windows 7 32 bits