The bug lies inside the Kohana framework and the used fpdf lib. Quick solution.
Edit the file
/omd/versions/1.6.0p12.cre/lib/kohana/system/libraries/Input.php
Starting at line 56 remove he two blocks
// magic_quotes_runtime is enabled
// magic_quotes_gpc is enabled
the second file is
/omd/versions/1.6.0p12.cre/share/pnp4nagios/htdocs/application/vendor/fpdf/fpdf.php
starting from line 1042 remove the next two lines.
Graphs should work but PDF export from PNP4Nagios is broken because there are other errors inside the fpdf lib.