Error in script

I am using php 5
I don't know what can I do.

Notice: Undefined property: MobileUserAgent::$screendims in /home/MobileUserAgent.php on line 592

Notice: Undefined property: MobileUserAgent::$imode_cache in /home/MobileUserAgent.php on line 581



public function imodeCache() {
return $this->imode_cache;//line 581
}
public function screenDims() {
return $this->screendims;//line 592
}