I get the error 999999 when I try to run the Extract By Mask tool from ArcToolbox in ArcGIS 10. Using the exact same files the extraction runs in 9.3.
I've tried converting my mask from feature class to shapefile, and nothing has worked. It gets to the "Converting features..." message in the tool, and fails:
ERROR 999999: Error executing function.
Failed to open raster dataset.
Failed to execute (ExtractByMask).