Not my mistake this time but something that I did miss. In my recent game against David, he combat squadded his Tactical Squad as they got out of a wrecked Rhino. Now, I'd seen Andy combat squad out of a Drop Pod before so I assumed that this was okay. However, there it is on page 51 of the Space Marine codex, your decide if you're combat squadding when you deploy. A simple mistake and one that had no bearing on the battle. In fact the only reason I looked it up was because I'd been thinking about the game for some posts and remembered that he asked if he had to take a pinning test for each combat squad (I said yes and he passed them both). From a tactical point of view I'm not really sure why he wanted to combat squad at that point anyway. Still, this is incredibly minor and I've only really posted it to point out that I feel like I'm still learning rules all of the time lol.
Actually, point of order - when the Space Wolves got their first WD army list back in 1992, they were actually the first Space Marines that were allowed to Combat Squad. In fact all of the wargear options for Grey Hunters and Blood Claws were selected and paid for in terms of a five man combat squad even though the pack was 10 strong. Of course these days, the Space Wolves don't need combat squadding anymore so that's my reasoning for not being totally up to speed.