Well, for one thing, in your screen shot the plane looks like it's sitting on the water rather than in it. That calls for a contact point adjustment, but it's not what's keeping it from taking off.
It could be an airport problem. First, try an Ai seaplane that you know works, and see if it works at the seadrome where you're having trouble with the Wal. If it does, the trouble is with the Wal. If it doesn't work, the trouble is with the airport.
If it seems to be the airport, load the AFCAD file into AFCAD (or the ADE9X file into ADE9X, or whatever airport file you're using into whatever program you made it with) and run the fault finder. That might identify your problem.
If not, it might be the runway surface, which probably wouldn't show up as a "fault." Eons ago, when I first started fiddling with AI back in the early years of FS9, I read in a tutotial that AI aircraft will only recognize concrete runways. I believed it and have always acted accordingly, so having never put it to the test, I can't guarantee that it's correct, but following that rule has never led me astray.
A concrete runway in the water doesn't seem intuitive, but it works for me (and for whoever wrote the tutorial I learned it from.) Don't worry about it looking strange, because it won't look at all - it will be invisible. That's because you give it a width of zero.
In AFCAD, the interface won't allow you to set zero as the width, but you can fool the program. Make the width zero point a few zeroes one, something like 0.001, and AFCAD will make it zero in the sim, making the runway invisible. ADE9X seems unwilling to fall for that trick, and in fact requires runways to be a certain minimum width - four feet if I remember correctly. The way around that is to make seadromes with AFCAD.
Getting your runway link (which can have a zero width and an "unknown" surface) to run directly on that zero width runway is tedious but possible, and if being off by a hair is the only fault that Fault Finder finds, the airport can work with that. Getting your start points on the runway is also tricky, but possible. I find it helpful to start out with a width of one foot, get the runway link and start points set, them reduce the width of the runway to zero. It's worth the effort, because if you don't get the runway width down to an apparent zero, you'll see a gray line on the water that won't do any harm, but will poke you in the eye and annoy you when you see it.
I hope that helps if you have an airport (excuse me, seadrome) problem. If your seadrome isn't the problem, it must be the aircraft, and I can't help with that. Some planes just won't work as AI, but some might just need a tweak from someone more knowledgeable than me.