HP Ew2400 - JetDirect Print Server Administrator's Manual page 199

Reduce or remove sources of interference. Metallic objects can
absorb or attenuate radio signals, and devices such as microwave
ovens and cordless phones operate using similar radio
frequencies.
Reduce the distance between the printer and the Access Point or
wireless PC. This can be accomplished by:
moving the printer
moving the Access Point or wireless PC
adding an additional Access Point (Infrastructure mode only)
Elevate the Access Point's antenna. In most office environments,
elevating the Access Point's antenna will improve the range and
performance of all wireless devices.
Firmware Download Failure
HP ew2400 firmware upgrades must be performed through a
wired/cable connection. As with other HP Jetdirect print servers,
firmware upgrades may be downloaded using tools such as HP
Download Manager (Windows), HP Web Jetadmin, or FTP (File
Transfer Protocol).
If a firmware download failure occurs on an HP Jetdirect wireless
print server, simply restart the download process and try again. If
it is powered off/on, the print server will regain its previous
configuration prior to the download failure.
ENWW
Troubleshooting the HP Jetdirect Print Server 199