I recently installed SP2 on a SharePoint 2007 instance. In order to migrate SP2007 content to SP2010 you need to have SP2 installed. So when I installed SP2, another .NET application on the server got jacked and I got the “required permissions cannot be acquired” error when trying to access the site. The issue was that the WSS_Minimal trust level got applied to the custom application. So once I found the web.config that was controlling the application I upped the trust level to Full. That fixed things, but it also upped the trust level for SharePoint to Full. And of course we all know we can’t fully trust SharePoint, right? So after much googling, and changing the (COPY OF) web.config I just removed the trust level tag entirely and both SharePoint and the .NET site work like a charm!