I have such an error with TortoiseSVN on Windows. Apparently, the .svn folder has a small SQLite database file, which if you do not have write access will result in this error.
Since I used TortoiseSVN through the Windows shell menu (right-click) to get around it, I launched Windows Explorer . I used to go to the folder as an administrator and everything worked fine.
Another solution, of course, would be to grant write access to the user with whom you are trying to use TortoiseSVN.
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