I tried to reproduce your result and indeed it happens if the conversion table file isn't found. The --convtable switch takes the file as given, that means if the path is not absolute it is resolved against the current directory. You have given only the filename so it looks for the file in the current directory, regarding your given console output this is /dumphd-0.5, check if your conversion table is there too.
Looks like you made the console dump by appending the > operator behind the whole command, this won't work because it grabs only the output from the program at the end of the pipe (in your case mplayer), maybe its also a problem because DumpHD writes it output to stderr and not stdout, i'm not sure. Anyway, its possible to grab the output from DumpHD but i remember it is difficult and so i forgot how
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