Linksys Wireless Router :: WRT54GS Multiple Devices Not Able To Detect

I have a Linksys Wireless-G WRT54GS with SpeedBooster.When I turn on 3 devices on Wi-Fi ( for instance 2 Apple MAC Computers, 1 Windows PC, and a wi-fi printer ), in other words 3 to 4 devices, everything works fine.  BUT when I add another device later in the day ( lets say an iPad ), the iPad is not able to access the wi-fi connection.  I get a message saying that another device is already using the connection.If I reset the router, then the iPad will be able to get in along with 2 or 3 other devices.  If I try an extra device, I get the same problem.What can be causing this?  I was under the impression that the router can handle an unlimited amount of wi-fi devices.