how to show errors in order to fix them?

[win8win]

v1.3.8a,
admin/includes/application_top.php
find
error_reporting(E_ALL & ~E_NOTICE);
and modify it to
@ini_set('display_errors', '1');
error_reporting(E_ALL);

I have done this ,why still canot see the content of error in the backend,

but blank when clicking edit of a category or product.

[DrByte]

MUCH MORE IMPORTANT: You need to upgrade to a secure version of Zen Cart. Yours is not secure, and should not be used.

[davowave]

Of course you should upgrade but also if you look in your cache folder you will see debug logs which may help you in the mean time.

[schoolboy]

Upgrade now... or you will have a lot more to worry about than "simple errors"... a hacker can add DAYS and WEEKS to efforts to restore your site...

[DrByte]

Of course you should upgrade but also if you look in your cache folder you will see debug logs which may help you in the mean time.

davowave, that won't work in older versions. It must be done manually instead. https://www.zen-cart.com/tutorials/index.php?article=82
Hence the strong advice to upgrade.

[win8win]

thanks,I will upgrade first ,