According to
this (page 9) the problem may be due to a lack of processing power.
Maybe try closing down any applications that are running in the background and see if that helps.
EDIT:
Found this too
Q2 : How do I enable Encryption on my Airolinks wireless products?
A2 : For WLAN clients, you can enable WEP Encryption in the monitor tool to connect to WEP enabled Access Point or Wireless Router. You can enable WEP Encryption of Access Point or Wireless Router in the Administration page.
WEP and Speed
WEP will slow down your wireless network. Expect a 20-50% reduction in speed depending on the products you are using. The speed issue is the result of the added overhead to the data packets.
Encryption keys
Encryption comes in 64-bit and 128-bit key varieties. All your nodes must be at the same encryption level with the same key to operate. 40-bit and 64-bit encryption is the same thing; it's just a matter of how the manufacturer decided to label the product.
Q3 : What is WEP?
A3 : WEP stands for Wired Equivalent Privacy . It is based on the IEEE 802.11 standard and uses the RC4 encryption algorithm. Enabling WEP allows you to increase security by encrypting data being transferred over your wireless network.
When WEP encryption is enabled, there are two options: 64-bit and 128-bit. 64-bit is the same as 40-bit WEP. The lower level of WEP encryption uses a 40-bit (10 character) "secret key" (set by the user), and a 24-bit "initialization vector" (not under user control). So lower level 40-bit and 64-bit WEP cards are equivalent in encryption strength and compatibility.
Maybe try using a lower level of encryption to save on some processing and packet size.