If the script fails to playback in its entirety, error messages will be displayed to you within the script recorder. Right next to the 'Script' tab, there is a Run-time output tab. This tab will contain any error messages that may have been outputted while playing back your script. Whenever there is an error during playback, this tab is automatically focused, displaying the error in red letters.
You can use this output to debug your script. In this example, there was a 'SearchStringException' which means that the text we were looking for did not exist on the page.