After installing Version: 4.2.5.2 Build-ID: 61cb170a04bb1f12e77c884eab9192be736ec5f5 it appeaers, that all the fonts "DejAVu" seem to be deleted from the Windows/Fonts directory. We had this problem on 2 Windows7/64 installations, where this font is required by another application. Because the other application is in frequent use, the connex was immediately recognized. Copying the fonts back from an alterant site fixed the problem.
I'm not quite sure how this is relevant to fontconfig. if you are sure it happened after installing something, ask them instead then.
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