Mr. Shumway: yes thats what i thought as well .. but it only occurs with characters with an ascii value of 128 (80) or higher .. and with all of them .. so it cant be an accidental loss of data

the databits are set to 8 in my program
i dont know how to check the databits of the serial port on the ipaq though .. it doesnt have a real serial port .. it uses a special cable to the normal connection on the ipaq (which normally ends in an usb connector :))

maybe the cable cant handle 8 databits ? but that would be weird as its serial data and not parallel so the data itself shouldnt matter

that leaves the driver (which is a default driver as i didnt have to install anything) or the serialport control in c# (or the functions i use to control the serialport) ?