If a script fails to play back successfully, there are several steps you can do to solve the problem.
For more information, refer to the Advanced scripting guide.
A script waits for the page in the Navigation action to complete loading. Make sure that the Wait actions are waiting long enough before the script tries to continue. Use the Wait setting to add additional time if necessary.
Verify that the appropriate type of Wait action has been used for the type of network activity. For example, only use a Wait for Page Complete if a new page navigation is taking place.
Sometimes the playback agent cannot use a locator during playback. The locator term may be too general to locate a specific element out of all the elements on the page. The website may serve different content depending on the browser. You may have to supply a locator for the element. Firebug, Firefinder, and the IE Developer toolbar are valuable tools for finding ways to create unique, valid locators.