You do not have permission to do this operation

I am a site collection administrator. When I go into SharePoint Designer 2010 I can see everything. However, when I edit a Master Page, or Page Layout, I get the following error:

You do not have permission to do this operation. Ask your site administrator to change your permissions and then try again, or log on with a user account that has this permission. To log on with a different user account click OK.

I have made sure that all the files on the 开发者_如何学运维site are checked-in/approved, and still no luck.

All Designer options are enabled in Central Admin.

Anyone have any ideas for things to look at, or try?

Try some of the answers given in this thread you do not have permission to do this operation + SP Designer 2010 Error