There are various possible causes.
- First of all, enable debug in conf.php.
- For debugging server-side or SQL error, use Firebug in FireFox browser or Developer Tool in Chrome browser and view the Ajax response in "edit.php". For trouble populating the grid, check the SQL returned from "data.php" instead.
Important: Do not refresh the webpage when debugging Ajax calls!
- Additionally, save will fail if a complex SQL query is used in C_DataGrid constructor, though the display should be fine. Complex SQL query currently does not support edit.
Microsoft IIS web server sometimes displays generic 500 internal error message. You must change the IIS settings to display server error in details with the following steps:
Error Pages -> 500 -> Edit Feature Settings -> "Detailed Errors"
If you are using IE, be sure to also uncheck "Show friendly HTTP error messages" in Internet Options: