You can't call serverside functions clientside.
My suggestion:
PHP Code:
// In your weapon
function onActionServerside()
{
player.triggerclient(params[0], this.name, this.itemDesc());
}
// In your GUI script
//#CLIENTSIDE
function onCreated() // or whatever...
{
triggeraction(0, 0, "serverside", weaponname.name, this.name);
}
function onActionClientside()
{
item_desc_text.text = params[1];
}