Show detection PLC connection loss in WinCC

Hi,

I've got a problem with showing a connection loss from my PLC. WinCC shows only mij loss if my PLC stands in STOP, so when I turn it of the picture isn't showing..
I've done the folowing:
Made a TAG in my PLC and connected in WinCC the following way:
options -> miscellaneous -> display -> Dynamic Dialog
there i fild in the folowing:
Expression -> " my tag"
Datatype: Boolean
Tag status -> Valid range -> No connetion -> Display -> Yes

So what am I doning wrong or what do I have to do to display/show an picture when I've lost connection with the PLC (Network error/ PLC failure/power loss etc)

Thankz in advance,

Roland