Here are the default login credentials in REXYGEN 2.50.x:
login: admin
password: blank
Use these when downloading your algorithm to the target device and also when accessing the web interface.
REXYGEN has its own user management system so do not use users/passwords which are setup in the OS (typically pi/raspberrypi on the Raspberry Pi platform), otherwise you get an error.
And make sure to change both the default passwords in REXYGEN and in the OS!