Roundcube doesn't send

[Tivaro]

My host (sevion.nl) has multiple webmail clients and I use roundcube. The've upgraded the roundcube (to which version I can't see) and since the update I can't send mail anymore. When I press the send button, the "Sending mail" message stays on screen but nothing happens. I've contacted my host but the said they couldn't find the problem (the settings were right they said (the other webmail clients work right.))