I'm trying to trade with my Crystal game, but it won't let me. Every time I talk to the girl to start the connection she says 'This room is reserved for 2 people linked by cable'. That's all she ever says! I thought maybe I was getting ahead of it with Crystal, so I tried doing them both at the exact same time but she still said that same thing. I know my link cable is good, I just used it yesterday to trade between Crystal and Red. I only have one Pokemon in my party on Crystal, which is an Abra with no held item and only knows Teleport. Why won't it let me trade? On Blue I'm in Cerulean Town. I just met Bill and came back to the Pokemon Center but I'm having this issue. Anyone know how to fix it?
I'm going to use you're using GBA hardware, including the link cable, but I'll cover all the bases here.
On Crystal, naturally, you need to ensure that you're using the "Time Capsule", not the trade centre. On Red, just use the normal trade counter.
Now then, as I'm guessing you're using GBA hardware, here's my "cut & paste" for every time trading issues comes up nowadays.
Linking Classic GB / GBC games via GBA
As Pokemon Red/Blue/Yellow/Green/Gold/Silver/Crystal were designed for the Game Boy & Game Boy Color, they were not designed for the GBA Hardware. As such, they cannot detect GBA Hardware, including the link-cables. You will require the Game Boy Color generation cable when trading over using any compatable GBA format.
The reason the GBA plays Game Boy/GBC games, is because there's a physical switch inside the cart slot that tells the GBA to switch to GBC mode, when a GB/GBC cartridge is inserted.
GBA systems compatable with GB / GBC games are;
GBA classic GBA SP Game Boy Player
Both the GB Micro and Nintendo DS/DS Lite lack the hardware (and the switch) to run GB/GBC games via legitimate means.
Here's what the cable itself looks like Whole cable (official) http://i791.photobucket.com/albums/yy198/gunbladelad/Game%20Boy/Linkcable.jpg