There is obviously something wrong somewhere. To find out you need to tell more about the issue. What you did, what you exported, etc. as it seems to work for most people here including me. Bug if any has to be repeatable otherwise I cannot do much.

The exporting usually works for me too, but now everything I export has this problem. I didn’t change any settings in blender, and I'm sure that’s not the problem because all my LEGO blender files still work and I can still import 3D Meca Bricks models that I have saved to my computer and they work perfectly. However when I export one of those same models form the workshop again, it doesn’t have the proper materials. It seems to be getting worse because now when I export something and open it in blender it has no materials.

Something else I have just noticed is that materials usually are named something like "mb_24" but now they are called things like "140:::".

Are you using the newest version of the Blender Lite or Blender Advanced Addons?

http://mecabricks.com/en/shop/product/2 and http://mecabricks.com/en/shop/product/4

As Masman8675 wrote, it looks like you are not using the right version.
Add-on has been updated less and a week ago as well as the workshop and it is not backward compatible. It has been mentioned in the special Add-on thread on the forum.

Thanks to both Masman8675 and Scrubs, I didn't know this. I installed the latest version and everything is working again. Thanks again!