Provide a SHORT reproducing script. You don't need to define any functions, etc. to test this. (6 lines?)

The error was fixed by restarting IIS.

apologies, here's a better version of the code with hardcoded values:

$font = imagepsloadfont("C:\\PATH_TO_FONT\\font_file.pfb");
$header_img = imagecreate(320, 20);
$font_color = imagecolorallocate($header_img, 42, 86, 143);
$bg_color = imagecolorallocate($header_img, 255, 255, 255);
imagefill($header_img, 0, 0, $bg_color);
imagepstext($header_img, "TEXT", $font, 18, $font_color,
$bg_color, 0, 16, 0, 0, 0, 16);

To reproduce, first run the code that work fine. Then introduce an error, run it. Remove the error, run it. The clean code doesn't work until a restart of IIS. There is a comment from 2001 in the docs about this on the imagepstext page...so this might be a T1Lib error that it can't recover from, and so wouldn't belong as a pure PHP bug(?)

New version of test script with <?php ?>:

<?php
$font = imagepsloadfont("C:\PATH_TO_FONT\font_file.pfb");
$header_img = imagecreate(320, 20);
$font_color = imagecolorallocate($header_img, 42, 86, 143);
$bg_color = imagecolorallocate($header_img, 255, 255, 255);
imagefill($header_img, 0, 0, $bg_color);
imagepstext($header_img, "TEXT", $font, 18, $font_color,
$bg_color, 0, 16, 0, 0, 0, 16);
?>

PATH_TO_FONT\font_file.pfb should be edited to work on the system used.

I can't really post on online version, since each time you run the script with an error, it would cause me to have to restart my web server.

The easiest way to see the error would be to point the $font variable to a non-existent pfb file, run it, then fix it to point to an existing pfb file. Once the error has occurred, the function no longer works even when the code is correct and the pfb file exists. Once you restart IIS, it works again.

This is propably some threading issue with T1lib..

Not PHP bug. Please report this to the T1 library author(s).