The exclamation is simply a notification that you have connected a non-LEGO® sensor into one of the EV3 ports. It does not interfere with the operation of the block.
This warning was removed in LEGO® MINDSTORMS® version 1.1.1.
The Vernier sensor block for EV3 MINDSTORMS can be found here:
LEGO® MINDSTORMS® Education EV3 Core Set with Charger, order code LEGO-EV3-CORE, $412
NXT Sensor Adapter, order code BTA-NXT, $39
Vernier Engineering Projects with LEGO® MINDSTORMS® Education EV3 (Electronic Version), order code EP-EV3-E, $40
TIL 3339: LEGO® Mindstorms® EV3 Troubleshooting and FAQs
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