'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 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?



Solution 1:[1]

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

Sources

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Source: Stack Overflow

Solution Source
Solution 1 Nikhil Vaghela