Rsview Studio Se Derived Tags

I am needing a way to produce an alarm when the connection to a plc is lost from inside the studio program. I tried to create a derived tag that uses the COMM_ERR(tag) function to do this and I can't get it to work. I have a hmi tag named cocomm which is also the name of the derived tag. In the tag editor cocomm is a digital tag with data source memory and intial value off. In the derived tag editor i put the expression comm_err(rslinx:tagname)--generic tag. I have stopped the derived tag file and restarted it to pick up the changes I msde but I get the error: item cocomm does not exist on any server. And I also get can not write value to derived tag cocomm. Any suggestions on how to get an alarm from a loss of communications to the plc either tell me what I am doing wrong with the derived tag or is there any other way to achieve this through events or macros?

Are you typing the expression, or are you letting the expression editor generate it for you?

If I remember correctly, the derived tag window doesn't have an editor. I opened an event, and used the editor in it to develope the expression using the pull-down choices. One the expression was formated, then you just copy/paste it into the expression window of your derived tag. Once your done close the event, but don't save your changes since it was just a workspace.

The reason I asked ws because you showed dashes (--) for what I think should be equal signs (==). If you can copy/paste your expressions into the topic here, it would help.

The -- was just to show that the rslinx:tagname was generic and not the actual tag that is being used. The derived tag editor does have an expression editor where you can browse to the function commands and also bring up the tag browser that has all the topic I have configured. So to answer your question no I did not type it in I used the browsers.

Are you sure there isn't a builtin way to alarm on a loss of comms?

I have taken it that the COMM_ERR(tag) is the only builtin way to tell if you have a comm fault to a plc. Please tell me if I am wrong.