Hi Stefan –
I’m glad to hear it is working now. My best guess is that the file was uncompressed at some point, but retained the .gz extension. The file readers that I use in the GUI and command line tools will open files whether they are compressed or not, regardless of the extension, but the readers used in BDP will explicitly decompress .gz files before processing them. If you are curious and still have the original file, you could check whether or not the files is the same size as your uncompressed volume.
thanks,
David Shattuck