Selenium IDE testcase -youtube

Hi all,

I am currently studying Video 8 (Selenium IDE) I tried testing youtube using Record and Playback Mode. I see the below error.Can somebody tell what this error means.

info] Playing test case youtube
[info] Playing test case youtube
[info] Executing: |open | / | |
[info] Executing: |click | id=masthead-search-term | |
[info] Executing: |type | id=masthead-search-term | barney |
[info] Executing: |click | css=span.yt-thumb-simple > img | |
[info] Executing: |click | css=button.ytp-play-button.ytp-button | |
[b:a7mnx1kw][error] Element css=button.ytp-play-button.ytp-button not found[/b:a7mnx1kw]
[info] Test case failed

TIA!
Asha