several functions failing
 

After having functioned almos flawlessly for over 2 years* our forum has many failing functions since today.

A few of them:
- when posting a reaction* an empty screen (and a 500 error) is the result. Depending on the usergroup* the reaction is or is not added* but the screen output is always failing.
- registering produces an empty screen as well (probably also with a 500 error). The user is added to the 'awaiting email confirmation' user group. The email confirmation request is not sent.
- submission of the 'contact us' form: same sort of problem.

I contacted our provider* and we didn't find the problem. I personally suspect a software update or a new setting* the total website (www.msweb.nl) has been down for a little while before the problems started.

The vB installation is not changed for months.

I hope there is someone around here who can help me find the right way to tackle this problem!

Further info:
http://www.msweb.nl/phpinfo.php
http://www.msweb.nl/forum

Thanx a lot!