[TYPO3] Problem with page browser

[Andrey Shevtsov]

Hi everybody!
I have this problem. When I click a "folder" button near any "Startingpoint" 
field (any module) I'm having blank window, no page tree is there in it. 
Script browser_link.php doesn't return anything into its frame. What can be 
the problem?
This bug repeats on several projects for version 4.2.0.beta. I know that 
it's beta, but may be any advices?