Hi, robin, Sorry you're having bother. Looks like you're set up OK, and the forum seems to be behaving, so: 1: Try logging out and in again. 2: If still no good, clearing browser cache, or just the cookie for the site that's giving issues, worth a try (sometimes a cookie gets corrupted, sort of half-saved, and it causes niggles).
As a footnote, I can only trace two RAF Catalinas fitted with MAD, FP191 and FP258 and that was for tests.
Does this name ring a bell, ref my original post? I now think that Dr Sell was US boffin Dr Maurice Bell, a specialist in anti submarine war, who spent time with US PBY squadrons. It was the flying notes of Sqd Ldr 'Dizzy' Desmond that refers to Dr L.G. Parratt accompanying a 'Dr Sell' during the MAD trials at Helensburgh.