If you are experiencing issues with DataGrab please read this entire guide before creating a support ticket.

Always check the logs first ;)

DataGrab logs a lot of activity. By default it will log to the system/user/cache/DataGrab-import.log file. Each time an import starts, it will purge old logged items from the file to avoid compounding the file size. You can change the logging type by adding the following option to your config.php file:
$config['datagrab_log_type'] = 'file|developer|php|off';
'file' is the default value. You do not need to add this to your config file unless you want to use one of the other options.
If you set the log type to 'developer' it will log to ExpressionEngine's Developer Log that is accessible in the control panel. Go to Tools > Logs >Developer Log and review the log for any error messages. It may be helpful to fully clear the entire log, then run an import again to ensure you have up-to-date log messages.
If you set the log type to 'php' it will write to your server's PHP log file. Depending on your system and how you have PHP configured, this file path may not be in a standard location such as /var/log/. If you do not want to log to your database (e.g. ExpressionEngine's Developer Log) or the user/cache directory, then you should use the php log option. If you choose 'php' as your logging option you can also change the path if you use the following config option:
$config['datagrab_log_file'] = '/var/www/log/DataGrab-import.log';
Note that if you change the log file make sure the directory is writable. We do not provide support for system configuration settings if the log is not outputting to the value you've defined. This option will not set your entire php error logging to this file. It will only log DataGrab events and errors to this file. Other ExpressionEngine or similar PHP errors will continue to be logged to your system defined log file.
If you do not set this option in your config file DataGrab will continue logging to the DataGrab-import.log file in your user/cache directory as mentioned above. You can turn off all logging by setting the log type to 'off';
If you disable logging and create a support ticket, you will be asked to re-enable and provide a log output of the import issue you're experiencing. The php or default DataGrab-import.log file is preferred for support requests since I can not read your Developer log without control panel access.

Try the Import URL

If you attempt to run an import and the Status column does not render a progress bar, but instead renders an error message, or something that looks like the screenshot below, then use the Import URL option and attempt to run the import in a new browser tab. From there, the full error message will be revealed. It is also highly possible the error will be in your import log. Please include the full error message if you're creating a support ticket.