Try re-installing it. It fixed the issue for me, though I was having different error messages.
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Open System Preferences, right-click (or control-click) on the Network Link Conditioner and click “Remove Network Link Conditioner” to remove it.
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In Xcode got to the Xcode menu -> Open Developer Tool -> More Developer Tools…
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In the browser window that opens, grab the most recent Hardware IO tools .dmg
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Double click the “Network Link Conditioner.prefPane” on the disk image to install it.