As I reported on the Google TiddlyWiki group…

Problem: Version 2.5.2 fails to save backup on a network drive in a

<br /> Windows domain environment with IE7.

<br /></font>

I've got two empty TiddlyWikis.  One is v2.5.0 and the other is
v2.5.2.  I have saved each in the same folder on a network folder
(i.e. \\servername\sharename\foldername).  I have defined
txtBackupFolder to be "backups".  When I click Save Changes, 2.5.0
saves the file and saves a backup in backups; 2.5.2 fails.

No plugins.
Windows XP SP3
On a Windows network, using Windows domain security.
­Fails when browser is IE7.
It works with Firefox 2.5.1.

I used a text editor on the file, and inside the definition of
copyFile, I changed ­

    copyFile: function(dest,source) {
    copyFile: function(dest,source) {
        var browser=navigator.appName;
        if (browser=="Microsoft Internet Explorer")

and I pasted ieCreatePath from the 2.5.0 TiddlyWiki immediately after
the Main function.

With the work-around, it saves the file and it saves the backup file.