QUESTION:
Why do I get an error message on my SIMATIC Field PG when I access the COM1 interface via my application?

ANSWER:  
You might have set up a "PC Direct Connection" in your network environment, which is blocking your COM interface.

Please proceed as follows to be able to use the interface again:

Right-click the "Network Environment" icon on your desktop and select "Properties". In the window that opens you see all the network connections and direct connections that are set up on your Field PG. Select all the Incoming Connections and Direct Connections (Fig. 1) and then delete them with the Del key.

Fig. 1: Properties of the network environment.

Open the "Device Manager" via "Start > Settings > Control Panel > System > Hardware". Here, under "Ports (COM & LPT)", you will find the Communications Port (COM1) that you then right-click and deinstall. 

To have the interface recognized again you right-click it in the Device Manager and select the option "Scan for hardware changes". Windows recognizes the COM interface and reinstalls it.

If you have not set up any PC direct connections, then you might not be able to set up any connection. 
In this case too you deinstall the COM interface and then have it recognized anew. 

If after reinstallation you still cannot set up a connection, then please check your computer for the following software:

• Teleservice software (PC-Anywhere, Real Out, ...)
• Mobile phone software 
• Fax software
• PC card modem (with virtual COM port)

If you do have such software installed, it might happen that this software is blocking communication via the COM interface. You should therefore deinstall the relevant software and then try again to set up a connection.