Thank you for your feedback - it is really beneficial and I will share it with the development team! Hopefully there will be improvement in the messages soon!
Apart from that I would like to provide some insights on the topic. I guess you are also seeing the error in the Results tab when a test list result is opened. The message starts with "X tests were executed out of Y on 'test' machine" so the assumption is that the tests listed as unable to load were not executed at all. Though you are correct it is not clear what the reason for that is.
The truth is there could be different reasons for that which needs to be investigated for each specific case. What we request in such cases are the log files of the execution machine and the one which hosts the scheduling service. Both can be accessed in the Execution Status View
and I would like to mention it is recommended to clear the logs before starting the faulty execution.
Please let me know if you will need to further investigate the errors you have encountered. In case you would like to find out what might be causing the errors I will appreciate if you generate and send the mentioned above log files zipped via this thread.
Thanks once again for the valuable feedback - it will certainly help us enhance the user experience with Test Studio.