Hi,
Do you have the latest Acymailing version (currently 7.9.2) and K2 add-on installed? I'm asking this since this is an issue that was solved in version 7.7.5.
I noticed you have posted the same issue in another thread that was about adding alt text using the Joomla media manager. I've deleted that post, it also was not related to the thread. Please be so kind to post your questions only once and preferably not to old posts that are marked as solved. Thank you for understanding.