If editing an asset doesn't work on your Mumara Campaigns installation, then it's nothing to get panic. Mumara sends a PUT requests for editing the assets like sending nodes, contact lists, sending domains, etc. If it doesn't give any results then it means your server isn't satisfying the PUT requests. The short and quickest way to resolve is, add the following lines to your htaccess file
<Limit GET HEAD POST PUT DELETE OPTIONS>
Require all granted
</Limit>
It should work!
<Limit GET HEAD POST PUT DELETE OPTIONS>
Require all granted
</Limit>
It should work!