Seeing this error message is typically the result of including special characters in the name of your space. Your space name doubles as the tail-end of the URL of your space, so it cannot include any special characters like space, \ , < , > , . , @ , ? , &, etc. and any character outside the ASCII charset.
In order to gain access to your space, you will need to change the name of the space. To do this, you need to clone the space in question and use a name for the cloned space that does not include any special characters. For instructions on cloning a space, please refer to the Help Center article on copying a room or Space.