I've followed all these steps already:
After completing Sharpening the Sword, speak with Ailbeche (J-9 in Northern San d'Oria) as a level 50+ Paladin and he'll request a Giant Shell Bug.
Talk to Exoroche at (K-7) in Helbrot's Blades shop in Southern San d'Oria for a cutscene.
You are not required to be a Paladin after this step.
Return to Ailbeche who tells you Giant Shell Bugs can be found in Crawlers' Nest.
Obtain one or several Giant Shell Bugs. You can buy them on the AH, or follow the steps below.
From the entrance to Crawler's Nest, use exit A at (H-8).
On map 2, find the small alcove at (H-9). The ??? is tucked away in the far end. Check it to spawn Dreadbug, which will drop 1-4 Giant Shell Bugs.
Trade the Giant Shell Bug to Ailbeche.
If you have multiples and you are skilled at fishing up monsters, you can skip this step until after you fish up Odontotyrannus.
Obtain a fishing rod, then head to the small pond on map 2 of Castle Oztroja.
From the entrance, go through the Brass Door at (I-8) on map 1. To avoid the trapdoor, throw one lever and then quickly move backwards.
On map 3, use exit F at (G-7).
On map 7, use exit I at (I-7).
Head to (H-8/9) on map 2 to find a pool of water with Oozes in it.
Fish up Odontotyrannus using your fishing rod and Giant Shell Bug. You will lose your bait and obtain Odontotyrannus (Item).
Return to Northern San d'Oria and trade the Odontotyrannus to Ailbeche.
If you did not trade your Giant Shell Bug to Ailbeche before, do it now.
When I try to trade him (Trade the Odontotyrannus to Zaldon (H-9) at the Fisherman's Guild in Selbina to receive the KeyItemKnight's Boots) he just stands there.
Any ideas would be appreciated, thanks!