From memory, there can be several reasons for this error. One reason is to do with pasting special characters into input fields. This is fixed in 4.2.0, check out this post viewtopic.php?f=12&t=108&p=229&hilit=axs8205#p229
There are some troubleshooting steps here https://axesdocs.lansa.com.au/index.php ... N0ZWQiXQ== including how to generate logs.
Or report the issue to your local support team.