Error while opening Sentinel-2 in SNAP?

[ABraun]

are you sure you also have installed the internal updates (Menu > Help > Check for Updates)?

Please have a look here:

• Error: No valid tiles associated to product [MTD_MSIL2A.xml]
• No valid tiles associated to product [MTD_MSIL2A.xml]
• S2 L2A product cannot be read
• Snap can’t open the Sentinel 2B L2A data