Hi sabinholdings, welcome to the forum!
I don't believe Wingnut2.0 had an issue with it not starting, he was just inquiring about the nature of that log message. It's innocuous and really should be cleaned up. That warning is not really indicative of a problem. I would expect almost everyone can find that message on almost every boot.
So, let's try to get more information. What is the operating system? What version of Mango?
Windows command prompt can have a very peculiar behavior where it won't output to the console if you've made a click-drag selection in the prompt. If you click back in it and hit enter all the output comes rushing out. But, Mango would still launch and if you had the env.property to open a browser on startup (the default).
You could try navigating to the Mango/bin directory at the command line and running either
./ma.sh start //Linux / Mac
which would ensure we were seeing all the output should a crash-worthy event occur. Windows will often close the prompt in a situation where this is useful, but it's a good thing to try.
Other things to try could be redownloading the bundle from https://store.infiniteautomation.com/core and starting on a clean database (move the Mango/databases directory while Mango isn't running, then start Mango).