Internal Server Error after creating new admin account on Asustor AS5202T NAS

Im trying to install NextCloud on an Asustor NAS AS5202T
everything was going fine but after I tried to create a admin account in ran into this page.

Internal Server Error
The server was unable to complete your request.
If this happens again, please send the technical details below to the server administrator.
More details can be found in the server log.

Does anyone know why this is happening? I don’t know to to edit config files or anything on Asustor’s NAS.