Update: this is already solved in the newest daily builds: https://coronarenderer.freshdesk.com/support/solutions/articles/5000570015-daily-buildsLooks like we have a solution, but this will probably need a hotfix.
If you are getting this message, go to:
C:\Users\_username_\AppData\Local\Autodesk\3dsMax\2017 - 64bit\ENU\en-US\plugcfg\corona
There, find a file named like Config-4885458.conf (the numbers can be different).
In this file you should see a line saying:
String system.workingDirectory = "C:\\Users\\xxxxxxxxx"
Make sure that the line ends with quotation marks ( " ).
So if it is:
String system.workingDirectory = "C:\\Users\\
Then change it to:
String system.workingDirectory = "C:\\Users\\"
Let me know in this thread if it works, and also if it works after restarting the PC. If it does, we will add it to helpdesk solutions, and I will file a report on Mantis.