Windows_Zertifikatsüberprüfung
Checking for Certifikate Windows VISTA/7/8/10
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Press Windows-Key + R, type in certmgr.msc and press OK.

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Click the arrow next to Vertrauenswürdige Stammzertifizierungsstellen, click on Zertifikate and search for T-Telesec GlobalRoot Class 2.

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If you can not find the certificate you have to do
A manual for installing the certificate can be found here.