Look at Account Settings -> Server Settings in the middle of the page "when I delete a message:" If you have chosen "Move it to this folder: ..." does that folder exist? If you don't have a 'Trash' folder, let me know.

thanks for your response, still no luck with deleting messages problem. this problem just started without us doing anything different than we normally do,we tried deleting to trash but we still get the same message along the bottom of the screen thanks from Judy

For Account Settings -> Server Settings in the middle of the page "when I delete a message:" try these:

1. 'Just mark it as deleted'
2. 'Remove it immediately'

Do either of those work?

Tried both of these neither work , thanks again. The only way I've found that I can delete them is by going into our main talktalk server.