Seems that the problem is caused by function join_paths() in class.fs.php. For details refer to line 281:
$retval = array_unique(array_merge($retval, preg_split('/[\/\\\]/', $segment)));
Here, all url segments are merged and every duplicate is killed. As I noticed on my server, I have two directories named "www", so one "www" is killed out of the queue.
the second "www" is ereased by the array_unique and now all following rebuilding of a valid path fails:
$retval = /var/www/vhosts/webpage/httpdocs/wp-content/
Now the exception is thrown. I thought about a short workaround in class.mvc_view.php, replacing the $retval assignment starting at line 242 with the following line:
$retval = $this->object->get_registry()->get_module_dir($module) . '/' . $settings->mvc_template_dirname . '/' . $path;
now this thing works fine, but now I have several other problems. I did a rollback on my live system and now I'm testing on my development system again. I'll test again, when the error above is fixed, maybe other calls are done for join_paths() from other places, too and so some of the other following problems are caused by this.
Hopefully this helps you fixing the problems