Connecting to Wireless networks

Hello,

I have a macbook pro. I connect to most wireless networks just fine. At my office our wireless is through one of our iMacs. The issue is that my MacBook Pro won't accept the wireless password. Every now and then others will come in and try to connect to our wireless and it also says they have the wrong password. Is this a problem through the iMac or do the people trying to connect have some sort of firewall up that doesn't allow them to connect?

Note: This issue doesn't happen to everyone but does happen to the same computers, iphones, kindles, nooks, ipads, etc. And not very many at that.

Any help would be appreciated.

Thank you