The only time I've seen this, it turned out to be bad ports on the unit. Have you removed and re-installed the driver per the following instructions?
http://knowledge.digi.com/articles/Knowledge_Base_Article/How-to-install-the-Edgeport-driver-in-Windows
Do you have another host to test this on?
If the behavior is seen on multiple hosts, the unit is likely in need of repair.