I made a master page and created a new page from it. In the PlaceHolderMain I added a few WebPartZones and then in the browser filled them with CEWPs and filled the CEWPs with content. Now I go back to SPD to add more WebPartZones to the PlaceHolderMain (Custom) I seem to be locked out of adding things. I can make changes to inside the existing WebPartZones and to the CEWPs but nothing outside of it. Any idea how I can "unlock" this again to add more so I dont have to "Default to Masters Default".
By default when you open a web part page and a page layout in SharePoint designer it's opened in safe mode which means you can only change the areas which you can also change in the browser.
What you want instead it to right click the page layout and select Edit File in Advanced Mode: