HP has issued an advisory for the iPAQ 4155. The problem is as follows: The request for a user certificate may fail on the iPAQ h4100 Series Pocket PC. If the user tries to secure a certificate via an 802.1x network on which the default configuration has been changed, the certificate request fails and the an error message "SendCertRequestToWebServer Failed" displays.
A software patch is available at the link below.