when you buy VMS Plat Suite, you'll get a specific serial number for NewbluFX . Use it for registering the product, and the red cross should go away. It was 2am when I installed the programme, so I may not recall every detail, but I think there was a 'nag screen' when I first used a NBfx plugin. I had to enter my email and my serial, and then the nag disappeared.
Generally speaking for bundled products, the serial number is requested during the installation process. It could also pop up when first added to a clip. Another place to look would be to add to a clip and click on the "i" button on the effect dialog. This will open up the info screen.
Also, if you're getting a circle with a red line through it, you're trying to drop the transition somewhere the transition cannot go. Take two clips, overlap them and the "X" area will form. Drop it on that "X".