Marcel, I'd suggest following this guide to troubleshoot definition update issues:
I keep getting a "Failed to update definitions" notice. It also happened last week. I was told to uninstall and install again but that does not seem to have worked.
I have a Zoom patch that won't install and now my daily scan is not working (since April12th)!
Marcel Levesque
Update Threat Definitions
cannot download Threat Definitions updates (message) Failed to check for definitions
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