I agree that this is not a very informative error. This error means that one of the Postscript FontDicts in the source font is defined, but is empty, which is illegal in font data. If you are not working with CID-keyed fonts, then this must be either the TopDict, which contains things like the font PostScript Name and the FontMatrix, or the Private Dict, which contains the values which affect hinting. If you are working with CID-keyed fonts, then the offending Dict could be any of the FDArray FontDicts and Private Dicts.
You should be able to use the FDK command-line tool 'tx" with the command-line options "tx -dump -o <path to source font>" to see the contents of the Font Dicts. I expect the problem is an empty PrivateDict, since it is really hard to make a Type1 font with an empty TopDict. If you are working with regular Type1 fonts rather than CID-keyed Type1 fonts, then you can either edit the font with a tool like FontLab, or use the "detype1" and "type1" FDK command-line tools to decompile/recompile to text , end edit the text version directly. The one required value in the PrivateDict is the BlueZones field. See the Type 1 Font Format spec at:
http://www.adobe.com/devnet/font/pdfs/T1Format.pdf
