# MATLAB: “Unable to locate compiler” mex error when using Visual C++ 2010 Express SP1 on 64-bit Windows

64-bitMATLABmexvisual c++

I had a working combination of Visual C++ 2010 Express and Microsoft Windows SDK 7.1. After installing Service Pack 1 for Visual Studio, I now get the following MEX error:
Error: Could not find the compiler "cl" on the DOS path.        Use mex -setup to configure your environment properly.      C:\Program Files\MATLAB\R2010B\BIN\MEX.PL: Error: Unable to locate compiler.
How can I get back to a working configuration?

Error: Could not find the compiler "cl" on the DOS path.        Use mex -setup to configure your environment properly.      C:\Program Files\MATLAB\R2010B\BIN\MEX.PL: Error: Unable to locate compiler.