WiFi shield not present (Maixduino)

I was testing several examples with Maixduino board. Some ran ok, others didn’t.
For example, wifi ones, like ScanNetworks, sent these messages:

[WiFiEsp] >>> TIMEOUT >>>
[WiFiEsp] Cannot initialize ESP module
[WiFiEsp] >>> TIMEOUT >>>
[WiFiEsp] No tag found
WiFi shield not present

Any tips?
Thanks in advance,
Carlos