Some forums require licensed ownership of a product before you can access the official support area for the product. In order to gain access into the licensed member areas of the forum, a registration number needs to be provided.
Why does Flight1 require this extra step for forums? This is because the Flight Simulation industry is suffering a very high level of piracy, and in order to only give support to licensed members, extra steps are required. This also assures that the forums are faster due to server load only being among legitimate licensed members and forum staff.
We wish we did not have to go to the above extra steps, but until the piracy situation improves, these steps are necessary. But we do hope the benefit of this is that the forums remain very informative, with an active community following of your product.