Can't log onto network

[Stinky The Clown]

One of our MacBookPros can't log onto the network. All the others can, but this one can't seem to have the network accept its passwords.

We have two networks, each with WPA Personal encryption. We are more than certain we are entering the correct passowrd, but we keep getting a message saying the password is invalid. The guy at the Genius Bar was unable to fix it. Our neighborhood Mac genius, former Apple Store employee, trainer, and expert, and current network engineering student couldn't figure it out. We tried a LOT of things and nothing worked.

The hardware is okay because the computer logged onto the Apple Store open network, no problem. As a test, I fired up my airport express as a test. This computer has never been connected to that before, so we thought, after removing the password, we'd see if it could connect to that. It did not.

This has been exceedingly vexatious.

Does anyone have a hint of what else to try or where else to look?

[Stinky The Clown]

1. Problem solved

After a second trip to the Mac Store and armed with suggestions from our neighbor, the problem was resolved. The guy at the Genius Bar deleted the machine's System Preferences folder. Upon a reboot, all Macs rebuild this folder (with the defaults of course, not with any custom stuff you set). Once booted, the machine logs on to all networks normally.

[cbayer]

2. Is there any drawback to doing this. I am having all kinds of

weird and intermittent problems and would be willing to try it.