msvcr100.dll
This file belongs to Microsoft Visual C++ 2010 Redistributable. Install that package and the DLL arrives with it, in the right place and correctly registered.
The error names your specific file, but the fix is the same for the whole family: every Visual C++ runtime file and which redistributable ships it.
If the file is already there and Windows still complains, read the message again: “entry point not found” is a different problem from a missing file, and installing the runtime again will not solve it.
And if the box says RUNDLL rather than naming a program, the fix runs the other way: something left an instruction behind pointing at a file that is meant to be gone, so restoring the file is the wrong move.
Do not download this DLL on its own
Searching for a missing DLL by name leads to sites that hand you that single file. It is one of the oldest and most effective malware delivery methods there is, and a system DLL from an unknown source is indistinguishable from a deliberately modified one. There is never a legitimate reason to obtain a runtime component that way.
The same goes for the tools that offer to do it for you: what a DLL repair tool can and cannot actually fix.
What it is
The C runtime from Visual Studio 2010. Programs of that generation still link against it, and no newer redistributable includes it, because each Visual C++ version installs side by side.
Where you see it: Software and games released roughly between 2010 and 2013.
Installing the newest Visual C++ redistributable does not fix this. You need the 2010 package specifically, from Microsoft's own download centre. We do not index it, so we have no verified download to give you, and we are not going to send you to a third party for a file this heavily targeted by DLL download sites.
We do not index this package
We have no verified download to give you for Microsoft Visual C++ 2010 Redistributable, so we are not going to point you at one. Get it from the publisher directly. That matters more than usual here, because this is precisely the file the DLL download sites target.