This is called the issue manager. You have at least one fault in your airport which would cause a compile failure. Click on the red button and it will open the issue manager and help you fix the fault(s). When all the faults are fixed it will turn green.
In ADE go to Settings/Options/Folders tab, click the ... button on the BglComp Folder line and browse to your copy of BglComp.exe. This file can be found in the FSX SDK (version SP1A or later, preferably SP2 or later) if you own the Deluxe version of FSX and have installed the SDK. Note that the SDK provided with Steam FSX is incomplete and may not include it. If you don't have the real FSX SDK, you can instead download and install the P3D 1.4 SDK (not the latest v4 SDK), which will create FSX compatible models.