This is usually caused when the driver "msg32" is disables in your computer. ( Or has been erased )
Solution: Go to Start/Run Type in "msconfig"
and open the Tab " Startup", on this list look for MSG32,
is there a check mark in the box to the left? If no, click on the box. Restart your computer.
If there is no MSG32 file , reinstall Giga or GigaVI ( please get the latest version from the tascamgiga.com site.