When I change an objects name, an error window pops up

When I change an objects name, an error window pops up:

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File Without Write Permissions - QT Creator

The following files have no write permissions. Do you want to change the permissions?

Filename: ui_mainwindow.h         Path: (my project path)

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When I click the button 'Change Permission', I get this window:

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Cannot Set Permissions - QT Creator

Cannot set permissions for (path) to writable. Aborting replace.

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I have uploaded images of the message windows.

Also, as far as I can tell, the file 'ui_mainwindow.h' does not exist.