TCDPF render a pdf with a png image, problem with transparent png

If i render a pdf with a png file, i get the following error.

What's the problem with this?

Warning

Message: imagepng(/...examplepathfolder.../tmp/__tcpdf_172a5566d5e348eba254a398c0909340_imgmask_alpha_2e51083373b9767f3e6183dfb1d0d48e): failed to open stream: No such file or directory

Filename: tcpdf/tcpdf.php

it seems that is a problem with a transparent png file if i try the same with a jpeg there is no error.

There is an example to work with transparent files, https://tcpdf.org/examples/example_042/

For me i wont't understand what i have to change with my code

$info_left_column .= pdf_logo_url();
$pdf->MultiCell(($dimensions['wk'] / 2) - $dimensions['lm'], 0, $info_left_column, 0, 'J', 0, 0, '', '', true, 0, true, true, 0);

pdf_logo_url() returns the absolute path of the png file.

Solution

omg i found the problem.

So, under normal use the temp-folder ("K_PATH_CACHE") is not in use for tcpdf. If you use a png the temp-folder is important to create a second image to prepare problems with the alpha-channel. So, in my installation was a wrong temp-folder, so i changed it and now all works fine :-)