Please explain in detail:

• what you're doing
• what happens
• what you expect to happen

I type an email in Thunderbird, I hit attach and browse for the file to attach. I find the file and attach it. The file shows up in the email, like it has for years upper right corner in the attachment box. I always click on the attachment to open it to be sure I have the correct file. Before the file opened and I could check to be sure it was correct, then close it and send. Now I get a window that pops up saying "There is no program, no file path". The file is displayed in the popup window but has a number added to the end, a wrong file and no path. I have sent the email to my self and I receive it with the attachment, when I try to open the attachment I get the same popup saying no program no path. The only way I could send the file is to past it into the body of the email. I don't know how the receiver dealt with it, I guess cut and past into word, I have received other attachments but they were pictures in the body of the email.

Try to start Thunderbird in safe mode. https://support.mozilla.org/en-US/kb/safe-mode-thunderbird

It did the same thing, I even sent the email to myself again and both when I compose, attach and try to open before I send, and when I receive attachments I can not open them. I get a popup window with the "No Application found" which includes a file path across the top of the window. I am not real geekie so solutions can not be overly that way. What about reinstalling an older version and forgetting the current one, and how is that done, I could not find older versions??

Very frustrating after ten years of using the program.

I may have misunderstood your problem.

Are you having difficulties sending a message with the attachment, or opening the attachment from the received message.

In the latter case see http://kb.mozillazine.org/Actions_for_attachment_file_types