I noticed a problem when attempting to attach a file to an existing message or comment from a client account. Specifically, this error is thrown with debug turned on:

Fatal error: Using $this when not in object context in /ux0/activecollab/test/application/models/project_files/ProjectFiles.class.php on line 148

Changing the line from this:

$conditions = array('`project_id` =? AND `folder_id` = ? AND `is_private` = ?', $project->getId(), $this->getId(), false);

to this:

$conditions = array('`project_id` =? AND `folder_id` = ? AND `is_private` = ?', $project->getId(), $folder->getId(), false);

does the trick.