Thunderbird freezes when saving message on the computer

Hello, It's been a few days Thunderbird freezes when I want to save a message on the computer (save as). When I close the saving window which is not responding, it automatically saves the message on my desktop. The file where the last message was successfully saved is still existing so I don't think it is a path problem. I have tried to restart it without the add-on but it doesn't change anything. And it is up-to-date. Anyone knows what the problem could be? Thank you! Estelle