I had a client call me up with a MOSS 2007 permission problem. The complaint was that users in a site owners group, with "full control" permission level, were unable to create a page anywhere in the WCM site collection.
Turns out that somewhere along the line the approvers group was deleted by mistake, which inadvertently removed read access to the Master Page Gallery. Adding the approvers group back to the MPG with read access fixed the issue.
I cannot take credit because I found the answer here.