When I add an existing source to an ISE project, the following message occurs:
"No Design units Detected in file"
Check the comments at the beginning of the file for information relating to turning off the synthesis tool.
You might see the following in the text:
Removing this text or renaming it will resolve the issue.
This problem has been fixed in the latest 10.1 Service Pack available at:
The first service pack containing the fix is 10.1 Service Pack 3.