Hi,
ok, I think I know how to solve it.
I had a few problems too. I upgraded from a previous version. Can't remember what version exactly and the problem was that the column 'secure_str' in my database was missing. Like the error message says. So I removed the extension completly. Deleted everything in the databased connected to the extension and then I installed it again.
Maybe you can just add the secure_str column by hand? I don't really know how the extension works. So if you want to keep your old attachments maybe you will have to do it by hand?! I don't know.
Another problem I had was that the value for the folder where the attachments are saved wasn't updated. So it still tried to upload the attachments to the old folder which didn't exist anymore.
But if you remove everything that shouldn't be a problem. Just don't forget to remove the values in the config table.