ASCII to Raster—Conversion toolbox | ArcGIS Desktop
many causes depending on the tool
maybe your nodata value isn't appropriate for your data type
spaces in the file path.
you didn't specify a file extension so an esri grid will be created (many errors associated with that)
many things if you didn't specify a folder location and *.tif file extension to save the raster in
Maybe you should copy the header and part of the first couple of rows.
Also, copy and past the location and raster filename so it can be checked