Today I faced problem with Testlink 1.9 – while clicking on Test Results > Charts I’ve got :
PHP Fatal error: require_once() [function.require]: Failed opening required '/var/www/html/testlink/cfg/.cfg.php' (include_path='.:/usr/share/pear:.:/var/www/html/testlink/lib/functions/:/var/www/html/testlink/third_party/') in /var/www/html/testlink/lib/bugtracking/int_bugtracking.php on line 367, referer: http://xxxxxx/testlink/lib/results/resultsNavigator.php
If you have similar edit /var/www/html/testlink/lib/bugtracking/int_bugtracking.php
Line 363: $btsname = strtolower($bts_type);
Dirty, but works

Still have no charts being displayed:
New install of Testlink 1.9.3 using defaults
Win2008 R2 Enterprise 64bit
IIS7 with CGI turned on
New install PHP with GD working fine
New install MySQL
Beginning to think that there is a Testlink PHP or Chart config install issue…
No Charts Displayed
Its a new install of TestLink 1.9.3 on A Redhat 2.6.18
Found the solution to the problem, on my redhat it was the out of memory because of the default memory_limit on my php.ini after changing it to memory_limit=512M and restarting httpd everything worked fine yey!