We recently found an issue related to backups including filenames with non-ascii characters which can cause this. This will only happen if a file which is included in the backup has been renamed to include a non-ascii character - PT4 doesn't have any of these by default.
The issue will be fixed in the next release, but in the meantime the backups are recoverable.
If any of the following doesn't make sense, or you get stuck, please open a
Support Ticket with a link to this thread and we'll work with you directly to sort this out.
Make a copy of the backup file before you do anything else.Do not touch the copy.
Open the backup zip file and edit the TOC.xml file in a text editor (e.g. Notepad).
You should see a list of filenames. If you can identify the filenames including non-ascii characters edit that filename to remove or replace those characters.
If the files aren't ones you want to recover (they may just be copies of files) then just remove them from the TOC.xml file (including the <name> and </name> tags around them, and you can skip the last part.
In the "Optional" folder structure within the zip you will see some filenames made up of long strings of random characters - these are the files that you just renamed in the TOC and you need to rename them here to match, as long as you can tell which file is which based on the file size and/or length of filename.
Once you've applied these changes to the backup zip file and saved it you should be able to restore it.
For example, in the example below the dash (-) in the "Kopio" (copy) files is a non-ascii character. This isn't obvious, but if you have similar filenames then that could be the issue if you don't see any obviously non-English characters.