When embossing directly to a local port (e.g. LPT1 or COM2), DBT sometimes reports a 'WriteComm failed' error. This means that DBT is having trouble understanding the handshaking signals coming back from your embosser. In simpler terms, it means that DBT and your embosser just are not communicating well.
The simplest way around this is force DBT to communicate with the embosser only through Windows. Very often, Windows itself will be able to write data to the embosser even when DBT is having problems. To do this, first install a Windows Device to drive your embosser. Then,using the Global: Embosser Setup... dialog, set DBT to emboss through a Windows Device and pick the newly installed printer driver from the list of available devices.
This process usually eliminates problems. However, if it does not, then you will want to look at the on-line help text for troubleshooting when Embossing through Windows Device fails.