admin/environment/php extension/ctype

De MoodleDocs

La extensión ctype está habilitada por defecto en PHP desde la versión 4.3.0. If it's not enabled on your server, either you have a very old version of php, or it was probably disabled at build time. You will need to either remove --disable-ctype from the build command, or add --enable-ctype. Read for details.

For details about Ctype features and history, you can read