When trying to open an attachment with Thunderbird, below error message appears on your screen:
[Thunderbird] error message:
"Unable to save the attachment. Please check the filename and try again."
This is due to a forwarded message that itself contain an attachment which however generates a bug under thunderbird. This is actually being worked by Thunderbird team which will be corrected for the future version.
Below is a temporary proposed solution
Click on View and then View attachments in messages .
If the first does not work, or if there are more than two messages, you can save the file on your hard disk.
Then right click on the file and click on Save as >OK