QUOTE (GMGough @ Jun 8 2012, 10:27)

In reply to: Could you check Tools>Options>Tags whether your the suffix of files is included in the list of file types?
Thank You. That works - I can now use mp3tag 2.51
What works now?
What do you have checked?
Did you change anything in the list of allowed file extensions?
Now, do you have two entries in the list of allowed file extensions?
For example ...
*.flac;*.FLAC;
This would be rather unusal and lead to other questions.
Why got the standard entry "*.flac" lost?
What type is your computer system?
Does the filesystem support case sensitive filenames?
Is it possible to use FLAC files, which previously cannot be loaded, to load them into Mp3tag, without modification of the list of allowed file extensions, after changing the file extension from possible uppercased ".FLAC" to lowercased ".flac"?
DD.20120608.1122.CEST