if file is empty, then you may have an error in the log file.
Please post it here.

My error log
2013-02-08 10:45:44 ** ERROR ** on file 'C:c:wampprojectorriaexternalhtml2pdfhtml2pdf.class.php' at line (1251)
2013-02-08 10:45:44 ** ERROR ** cause = ERROR n°1 : The tag <BUTTON> does not yet exist.If you want to add it, you must create the methods o_BUTTON (for opening) and c_BUTTON (for closure) by following the model of existing tags.If you create these methods, do not hesitate to send me an email to webmaster@html2pdf.fr to included them in the next version of HTML2PDF.
2013-02-08 10:45:44 ** ERROR ** => #0 C:c:wampprojectorriaexternalhtml2pdfhtml2pdf.class.php (1226) -> _executeAction()
2013-02-08 10:45:44 ** ERROR ** => #1 C:c:wampprojectorriaexternalhtml2pdfhtml2pdf.class.php (5446) -> _makeHTMLcode()
2013-02-08 10:45:44 ** ERROR ** => #2 C:c:wampprojectorriaexternalhtml2pdfhtml2pdf.class.php (1255) -> _tag_open_TD()
2013-02-08 10:45:44 ** ERROR ** => #3 C:c:wampprojectorriaexternalhtml2pdfhtml2pdf.class.php (1212) -> _executeAction()
2013-02-08 10:45:44 ** ERROR ** => #4 C:c:wampprojectorriaexternalhtml2pdfhtml2pdf.class.php (5446) -> _makeHTMLcode()
2013-02-08 10:45:44 ** ERROR ** => #5 C:c:wampprojectorriaexternalhtml2pdfhtml2pdf.class.php (1255) -> _tag_open_TD()
2013-02-08 10:45:44 ** ERROR ** => #6 C:c:wampprojectorriaexternalhtml2pdfhtml2pdf.class.php (1212) -> _executeAction()
2013-02-08 10:45:44 ** ERROR ** => #7 C:c:wampprojectorriaexternalhtml2pdfhtml2pdf.class.php (408) -> _makeHTMLcode()
2013-02-08 10:45:44 ** ERROR ** => #8 C:c:wampprojectorriaviewprint.php (136) -> writeHTML()
2013-02-08 10:45:44 ** ERROR ** => #9 C:c:wampprojectorriaviewprint.php (120) -> finalizePrint()
Thanks

OK
Issue is strange, and don't seem linked to number of lined to display.
I recorded issue as ticket #998.
Can you please check is one on your activities contain something that could look like a HTML tag.
There is an error about a tag...