Website doesn't work Well after update from RW6 to RW7

Hi dear,
I need your help.
I downloaded Rapidweaver 7,
I have 2 projects that I can not finish and publish.
The problem is next I am doing new web site and it get me a problem. I have 2 websites from Rapidweaver 6, I oppened them in Rapidweaver 7. The HOME page give a next problem. In the EDIT page down of the half page has pink color with next sentence’'This stack is not currently installed. You need to reinstall it to use it". When I press PREVIEW,dowm of half the page does not appear.
Before I did not have this problem , it was done sucsesfull, it is appear today.
I could not find the stack that I need to restore.
The Stack that I have installed was updated successfully, but the problem did not disappear.
What do I need to do?
Kind Regards

When you click on the missing stack, you should see some more information about that one on the right side inside the stacks plugin inspector.