Something in the ~/public_html/system/logs/error.txt *prior* that App Warning?
The warning itself is very common and can be seen in the log even on healthy Abantecart installation. The past records on forum indicate there may be different causes of it, even though the text of the warning is always the same; probably, it makes sense to improve this warning's reporting in the Abantecart by adding verbosity in the code as to what has caused the warning exactly(?)...
Your blank page suggests there may be a PHP error thrown. You can check if your "display_errors" PHP directive enabled by creating a .php file in your ~/public_html with this content:
<?php
phpinfo();
?>
Then check the output by calling it in a browser, something like freakytikihammocks.com/zzz.php
If that's found to be set to Off, you can enable it in ~/public_html/php.ini manually by adding :
display_errors stdout (for PHP >=5.2.4)
display_errors = On (for PHP <5.2.4)
Also, anything in Apache error_log or the Error Log thing in cpanel ?
