The popup appears when a file is open on the local computer, and another person has uploaded a newer version of the file.
The system is trying to replace the old version on the local computer, and the file is locked.
Just follow the instructions displayed in the popup (close and/or save the file currently open), and the popup will disappear with the new version being ready.
If this is not the case, it is usually one of the following:
1. The filename contains an illegal character. On macOS, it is fine to have ":" or similar characters in the file name, but not on Windows. Please rename the file via the webclient, removing the illegal character.
Find out which characters are illegal in our article about valid file, folder, and share names.
2. The share name or one of the folders in the path has a "space" character at the end. This usually happens when on MacOS, the user names a file/folder to something that already exists.
In this case, the MacOS will put a "space" character at the end of the file/folder to distinguish it from the original one. This is fine on the webclient/MacOS, but not on Windows.
Please use the webclient to rename the share/folders that have the "space" character at the end.