I was getting the same error, and what I tried and worked for me was to run cmd.exe as an administrator.
Microsoft Windows [version 6.1.7601] Copyright (c) 2009 Microsoft Corporation. All rights reserved.
C: \ WINDOWS \ system32> cd C: \ dev \ GitHub \ JspmTest
C: \ dev \ GitHub \ JspmTest> jspm -v 0.15.7 Run against a local jspm installation.
C: \ DEV \ GitHub \ JspmTest>
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