I suggest you to ask your question on stackoverflow and/or ask your question directly to engineers on github as you should get much better result in term of answers.
Server Fault is for system administrators and desktop support
professionals, people who manage or maintain computers in a
It is the problem of java iKVM Viewer. It for some reason requires a write permission to your iso file. If it is missing, then mounting fails.
I have accidentally found mentioning of such requirement from the very end of this article.