@bobsalive After extensive testing by borrowing a lot of vexnet keys from other teams, we found that apparently two of our vexnet keys are duds. They take a long time to connect with any other vexnet key, and then the connection cuts out quickly, with or without backup battery, with or without extension USB cable. Unfortunately it looks like we're going to have to buy two new vexnet keys, which is a problem because they're reasonably expensive and we can't afford them.
This has happened to my team (84) at a few of competitions, and including a couple of other Downingtown Vexmen teams. At worlds, while waiting to start the match, one of the members of the opposing team could not link up, then after many attempts to fix this, the field control people (tech support?) plugged in new keys and it worked instantly. Apparantely, faulty keys are not so uncommon and Vex should look to try to fix this, whether it is from dropping them or over-using/heating them, etc.. It is very frustrating and can take a while to figure out the problem. In our case, the key situation got very bad and when we could link up, nothing could be downloaded. No firmware (joystick, main CPU, or the other one) , no code , nothing. Not even the IFI loader would work at first.