PDF Export

It seems to be working fine except when I try to export a spreadsheet in .pdf format I get the following error and the .pdf file is corrupt.
Warning: Invalid argument supplied for foreach() in PHPExcel_Writer_HTML->_assembleCSS() (line 1315 of /sites/all/libraries/PHPExcel/Classes/PHPExcel/Writer/HTML.php).

1312 private function _assembleCSS($pValue = array())
1313 {
1314 $pairs = array();
1315 foreach ($pValue as $property => $value) {
1316 $pairs[] = $property . ':' . $value;
1317 }
1318 $string = implode('; ', $pairs);
1319
1320 return $string;
1321 }