Moss 07 suddenly cannot use designer to modify the page

Just created several master pages using SharePoint designer 2007, and then created the default. aspx page for the sub-site under the site set through the master page.
After creating a few items, the system suddenly jumps out of the box and says it cannot be modified.

I thought it was because my colleague logged on to the remote machine with the same administrator account, and thus I had no permission.
This is not the problem.

Then in the moss site set settings, we can see that the Administrator is "restricted access", so it is still fruitless to change it to "full control...

In a hurry, I restarted IIS (iisreset). Hey, all right! Wondering...

In retrospect, it seems that the master Page Management page of the site set has been used to operate on several masters. This may be the reason for checking in and out. Maybe.

Who knows? I almost want to restart the moss server.