Problem whit itoa - conversion integer to string

I tryed that itoa function in my sw webserver enc28j60 based work but only one time. It maybe demage some registers on webserver library and no more pages will be show after use of itoa funcion

Can you suggest me an alternative mode to convert integer in string please?

static char* stringa = "";

Ciao from Italy Sorry for my english

char myString[10]; 
itoa(H_Accensione, myString, 10);

I may be wrong, but you just defined a pointer, so there's no space alocated for your string. If you define an array, that won't be a problem. I think that 10 chars are overkill for this, bu it's better to be safe than sorry.

I may be wrong

You are not. You defined exactly what was happening. OP defined a pointer to nowhere, and asked the itoa function to write data there.