I can think of two possible reasons for your problem:
1) Your PHP version is lower than 5.2.4
2) Your server provider has disabled the php_ini_loaded_file() function
If you have something between PHP 5.2.0 and 5.2.3 you may try to just delete "<?php print php_ini_loaded_file(); ?>" from the source code as it is purely informational and not essential to program execution. You might encounter similar compatibility problems at other locations in the code, however, as Lemon8 has been developed in a PHP 5.2.4 environment (and later).
Unfortunately our download page does not state this requirement correctly. We'll change that.
BTW: Lemon8 is experimental software. We are no longer actively maintaining it. Its functionality (document and citation parsing and XML generation) will however be completely integrated into our OJS, OCS and OMP software. You'll also be able to use the document and citation parsing libraries stand-alone and integrate them in your own programs.
If you tell me what exactly you're trying to achieve I can give you a better recommendation of what I'd do in your case.