SD Init fail error: cannot send prints by Wifi ESP8266 module.

Hi,


I use a Ender-3 upgraded with a SKR Mini E3 V1.2 board and a TFT35-E3 V3.0 (both by BigTreetech).
Last week I added a Wifi ESP8266 module, in order to send prints directly from PC.
Everything went fine (I can move the printhead, monitor the temperature and so on) but I cannot send any file to the printer.


When I insert the SD in the TFT35 reader, on the display I can read the file names present in the card and print them without problems.


But from PC ( web gui ESP3D forMarlin) I cannot read any file name from SD (even if present). When I refresh I get an empty list.
If I try to upload a file to the SD I get a "SD init fail" error on the TFT and then a "Error 0:" on the PC.

Same "SD init fail" message if I try to "Init SD card" from TFT35 menu.
FW of TFT35 and ESP-01 module are both up to date. I tried different SD but no joy.
What's the problem here?

Thanks in advance.