How to check ajax text presence?

[Tropicalista]

In some page there is an ajax check to see if a login username is used or available.

If I try to parse the page to check if the text is there it never find the text.

How could I resolve? this happen also in gmail account registration, for example.

 

[Hungry Bulldozer]

Try click in such case on "Element reindexation" button.