I'd like to get a little more information about your system, as we are in the process of testing Windows 7 Professional with FlexiSign Pro 8.1 as well. So far, we have been able to cut to Graphtec and Mimaki plotters, but have not yet had a chance to do the test printing.
What is your printer, and how is it installed? Did you use the drivers from the mimaki website and install it as a Windows printer (so it shows up in the list of Devices and Printers) or did you only install the driver through the Production Manager configuration?