Wireless Network Connection Fails

We are running Windows XP network using a Cisco 800
Series Router and aironet 340 wireless lan adapter. When
we try to access an application on the desktop from the
laptop with the lan adaptor, the application tries to
open and then the connection fails. We can refresh the
connection but it fails each time we try to open the Act
database or the Filemaker Pro applcaition running on the
desktop. The internet connection also fails on the
remote laptop and other pc's remotely attached to the
desktop at random times.