Call to undefined method PrintTCPDF::AliasNbPages()

Using TCPDF results in an HTTP internal server error.
The Apache error log shows:
PHP Fatal error: Call to undefined method PrintTCPDF::AliasNbPages() in /mysite/sites/all/modules/print/print_pdf/print_pdf.pages.inc on line 289
TCPDF seems to be installed correctly. In the adminstration page the tcpdf.php is found in /mysite/sites/all/modules/print/lib
Drupal core version is 6.22
TCPDF version is 5.9.089 (2011-06-13)
Maybe recently changed? I did not use TCPDF previously.