It looks like it could be a consumed tag - from the limited screenshot I can't be sure, but it appears as if it's a consumed tag in a device called Motor_PLC. The fact that the tag is called "Read_From_Quad" would back this up.
If you import this tag, but the producing PLC is not yet configured in your ethernet tree, then you'll get this red X. Is there any chance that you initially didn't have Motor_PLC in your communication tree, and subsequently added it in?