What version of Thunderbird?

Version 38.7.2

Update to the latest version (currently 45.1).

Thanks. I found the auto download for 45.1 in april failed & I must have missed the notification of that. I have now down loaded . I have now linked a file & sent it to my self as a test worked ok. But when I tried to send the same file to Switzerland it would not work but small files were ok.Thanks for your help.

But when I tried to send the same file to Switzerland it would not work

When using FileLink you upload a file to the box.com server instead of attaching it to the message itself. You don't send a file 'to Switzerland '.

'it would not work' isn't a comprehensive problem description. You'd need to be more specific about what didn't work.

ok ,when I selected a file 11Mb in size & thunderbird said I should link it. when I did It sat there with the small circle icon by the file name in the top right hand corner rotating for a longer period than would be required for this size file. Then upload error message appeared saying [ unable to upload (file #) to. ] This happened again tonight with 2 separate addresses. Thanks.

Try to start Windows in safe mode with networking enabled. - Win10 http://windows.microsoft.com/en-us/windows-10/change-startup-settings-in-windows-10#v1h=tab01 - Win8 http://windows.microsoft.com/en-US/windows-8/windows-startup-settings-including-safe-mode - Win7 http://windows.microsoft.com/en-US/windows7/Start-your-computer-in-safe-mode

Still in Windows safe mode, start Thunderbird in safe mode. - https://support.mozilla.org/en-US/kb/safe-mode

Does the problem go away?

The link for win 8 comes up as page cannot be found. I managed to start imy win 8.1 in safe mode with networking enabled & thunderbird in safe mode. When I tried to send/link I got a message (failed to connect to server) I ran trouble shoot & was told to check outgoing server SMTP.Found Default server, mail.internode.on.net. port 465. my user name & pass word. connection security SSL/TLS.. Server settings the same but port #993. I hope this makes sense . Thanks

Did you start Windows in safe mode with networking enabled?

Is your network connection via WLAN? It seems Win8 disables the WLAN driver in safe mode, so you may need a wired connection.

Yes , started windows in safe mode with networking enabled &I have a wired connection to modem. This is strange as every thing else seems to work ok with thunderbird. I am thinking of stripping C drive , formatting & reloading win os from scratch. Thanks.

As an alternative to box.com you can try Dropbox as File Link provider. You'd need to install this add-on though. https://addons.mozilla.org/en-US/thunderbird/addon/dropbox-for-filelink

at last some progress, I managed to add on dropbox & it worked ok. I then loaded thunderbird to another computer with win 10 & added box & it worked. I then went back to the comp with win 8.1, removed dropbox, then added box & now it works. I plan to format & clean install the OS to make sure all the clitches are gone. Thanks for all your help.

When your problem is fixed can you mark the thread as 'Solved' please? Thank you.