Occurrence
ER Mapper header files (.ERS) can be linked to a number of data file formats including ECW or TIFF raster images. You will need to first convert these to a ER Mapper Raster Dataset before importing into Discover.
Solution
1/. Open the ER Mapper file (.ERS) in ER Viewer and use File>Save As to save it as a 'ER Mapper Raster Dataset'. This should produce 2 files; an .ERS file and a data file (with no file extension).
2/. In MapInfo Professional, use File>Open>Grid Image to select the converted file. During the import procedure you may have to choose a MapInfo Coordinate System that matches the reported ER Mapper Coordinate system and Datum of the converted file.
3/. This imported grid file can now be manipulated with the tools in the Surfaces Menu.
Note: TIFF files can be opened by simply File>Open>Raster Image, and ECW file should be opened by Discover>Import or Export>ECW/JP2 Import