Form Builder 0.6.4 not sending mails

[Druuna2008]

I have several sites using form Builder and for the first time the form is not sending mails. First it did (5 in total) and then it stopped without reason. At first I got the message - "message form empty", and then no message at all. It will only display the form, that can be filled out with no problem and that's it.
No read-only is clicked, cms mailer is properly installed and working.

I uninstalled the form builder, reinstalled it, nothing. Still showing the form, but not sending. Any idea what it could be?
The only changes I did in the mean time was the config.php for pretty URLs and the .htaccess for the same reason.
I'm running CMSMS 1.8.2

thx

[Dr.CSS]

You checked/changed the mail to addresses?...

[Druuna2008]

yes I did. As I said, it worked a couple of times and then without any apparent reason it startet to show the message "Message form empty", and then it even stopped to show that message and it just reloads the form. It's very strange.
It seems like it would not write the message content to the DB. However all other stuff is working and I even changed the permissions for all the module files to 777 and it still doesn't work.
Is there any alternative to form builder? I have to deliver the site on monday

[Dr.CSS]

Has your host changed anything, your sure the email send to template has stuff in it, have you checked every tab in form builder in it's main admin and the form itself?...

[Druuna2008]

Yes, I've checked everything. I even redid the templates to make sure the field names were all correct and in the templates. I also tried with the standard forms without changing them. And my hoster didn't change anything, we are running an own server, so I know if something had changed. There is no clue in the log either. 

[Dr.CSS]

Your CMSMailer sends test messages, right?...

[Druuna2008]

yes, it does

[Dr.CSS]

Well now I'm fresh out of ideas, unless I was in the backend...