There is a problem with the signature file. In a signature file, the series of layers or grids that were used to create it are identified in the #Layer-Number Grid-name list. In the list, the number of the layer in the input stack or series of rasters is followed by the name of the layer or raster. Either a layer number or a raster name in the list is wrong or missing.
Open the signature file and examine the Layer-Number and Grid-name list. If it is corrupt or incorrectly formatted, you can correct it with an ASCII editor, but it would be better just to re-create it. See Create Signatures, Edit Signatures, and Iso Cluster for more information on signature files.