Error: Failed to copy the specified file
The IHydrologyOp.Fill fails to work the second time in a single session on some datasets. The method reports this run-time error:
"Failed to copy the specified file."
This is a known problem with ArcGIS 8.1.
Solution or Workaround
This issue has been addressed in ArcGIS Version 8.1.2.
In ArcGIS 8.1, close the session and start it again.