 <p>It seems that your TFS Build Service account has no required permission to access the signingKey.pfx on build agent machine. Make sure you have this file on build agent machine first. </p> <p>Then follow below steps:</p> <ol> <li>Log on the build agent as <strong>your local build service account</strong> (Better have Administrator permission)</li> <li>Open a visual studio command prompt and <strong>navigate to the directory the key is stored in</strong></li> <li>Type command <code>sn –i signingKey.pfx VS_KEY_EFCA4C5B6DFD4B4F</code>(Ensure that you use the key name appearing in the error message)</li> <li><p>When prompted for a password type the password for the pfx file</p></li> <li><p>Then rebuild it</p></li> </ol> <p><strong>Note:</strong> If you are not running Visual Studio as an Administrator try doing that as well.</p> <p>More details you can reference the answer from <em>Brandon Manchester</em> <a href="http://stackoverflow.com/questions/2815366/cannot-import-the-keyfile-blah-pfx-error-the-keyfile-may-be-password-protec">Cannot import the keyfile &#39;blah.pfx&#39; - error &#39;The keyfile may be password protected&#39;</a></p>