I cant figure out what this is and how to solve it, can anybody help me.

the complete message is like this

(E:\Dokument\DBC-System\Utveckling\DOXY-ADIO\latex\main_8h_source.texpdfTeX war
ning (ext4): destination with the same identifier (name{main_8h}) has been alre
ady used, duplicate ignored
<to be read again>
                   \relax
l.3 }
      [159]

! Package inputenc Error: Keyboard character used is undefined
(inputenc)                in inputencoding `utf8'.

See the inputenc package documentation for explanation.
Type  H <return>  for immediate help.
 ...

l.116 }

? H
You need to provide a definition with \DeclareInputText
or \DeclareInputMath before using this key.
?