Hi Jakub,
That error you posted suggests that your XMR service may not be working. Please can you issue a reconfigure and see if that clears the error? You can then test XMR by requesting a screenshot, to see if it is returned before the collect interval. If it is returned before the collect interval, them you know that XMR is working and you can try sending commands again.
Please also note that there is a fix for commands in the latest Android player, which is R408 at the time of writing this message. Can you click on the link for R408 and upgrade to that version, to see if this also helps with your issue with commands?