I don’t like “sorry, but” constructs one single bit. They sound very patronizing and are a sign of failure of copywriter and UI language. If your stuff doesn’t work, then just say so. Mitigating this could be as simple as removing the “but”. “We’re sorry. We can’t do this for you right now.” sounds much better to me than “We’re sorry, but…”. Obviously, even better would be if there was no error in the first place… but if there is, no matter what you message, the user is pissed anyway, so no need to further patronize with “but” – just say it’s broken and it will be fixed and then do as you say and fix it.