Some customers have reported that the clear plastic piece attached to the right side of the moving tool carriage block (the "Guard") fell off. After consulting with Cricut Support, here are the steps to re-attach the piece on the block.
Step 1. Align slot in the guard with the white support tab on the carriage.
Step 2. Engage slot in guard with white support tab on carriage. Guard is slightly higher than tab. Push guard toward the back of the machine.
Step 3. Guard is pushed back but still high.
Step 4. Push down on the guard with a finger until it clicks.
Guard is in position on the carriage.