Objects not found on first run

I've got a weird issue going on with a script which is getting quite frustrating.  The script opens Chrome, navigates to a page and does a Global.DoWaitFor('Search');  It's waiting for the main search button to appear on the page so that I know the page has loaded.  After this it verifies the search button is enabled and that the text is correct. 

The issue I'm having is that the first time you run it you get an object not found error on the verification step.  If I then re-run the script leaving the previous failed chrome window open, the script successfully opens a new Chrome window, navigates to the page but this time finds the objects and passes.  This happens every time if starting from a point of no Chrome window open. I have tried adding in a Global.DoSleep and upped it to 15 seconds (15000), but still no luck on the first run.

Any ideas anyone?

Cheers,

Amanda