When we upgraded our PHP version to 5.5.3, we had problems with TCPDF using the live version of Piwik.
Upon researching, the only solution we found was in version 2.0-b3 so we installed it instead.
The PDF file under Email Reports was created when downloaded manually.
The problem is the reports where not being emailed automatically.
So we checked again the settings and tried to download it again manually and here is our new error :
Warning: Illegal string offset ‘masked’ in /var/www/http/piwik/libs/tcpdf/tcpdf.php on line 7067
#0 Piwik\Error::errorHandler(…) called at [/var/www/http/piwik/libs/tcpdf/tcpdf.php:7067]
#1 TCPDF->Image(…) called at [/var/www/http/piwik/libs/tcpdf/tcpdf.php:7265]
#2 TCPDF->ImagePngAlpha(…) called at [/var/www/http/piwik/libs/tcpdf/tcpdf.php:6970]
#3 TCPDF->Image(…) called at [/var/www/http/piwik/core/ReportRenderer/Pdf.php:385]
#4 Piwik\ReportRenderer\Pdf->paintReportTable(…) called at [/var/www/http/piwik/core/ReportRenderer/Pdf.php:318]
#5 Piwik\ReportRenderer\Pdf->renderReport(…) called at [:]
#6 array_walk(…) called at [/var/www/http/piwik/plugins/ScheduledReports/API.php:445]
#7 Piwik\Plugins\ScheduledReports\API->generateReport(…) called at [:]
#8 call_user_func_array(…) called at [/var/www/http/piwik/core/API/Proxy.php:199]
#9 Piwik\API\Proxy->call(…) called at [/var/www/http/piwik/core/API/Request.php:205]
#10 Piwik\API\Request->process(…) called at [/var/www/http/piwik/plugins/API/Controller.php:34]
#11 Piwik\Plugins\API\Controller->index(…) called at [:]
#12 call_user_func_array(…) called at [/var/www/http/piwik/core/FrontController.php:114]
#13 Piwik\FrontController->dispatch(…) called at [/var/www/http/piwik/index.php:56]
Please help. We rely on Piwik for analytics on ALL of our websites.