I open a project and the following error occurs:
"ERROR: [#UNDEF] File not found: <PATH>/runs.xml"
This error occurs if the project and runs directory content get out of sync. Usually, this happens on Windows when some process keeps a lock on the <project>.runs directory (e.g., antivirus programs). In these situations, you typically see that the <project>.runs directory contents have been emptied out, but the "runs" directory itself could not be deleted. Instead, the most recent data would be stored in a runsXX directory (see below).
In ISE Design Suite 13.1, automatic recovery mechanisms have been added to get around this issue.
In 12.x, the following work-around can be used: