Path not found using CreateProcessW in C

Why does this code return 2, which is ERROR_PATH_NOT_FOUND?

int runCmd() 
{
    char buff[]  = "c:\\windows\\system32\\cmd.exe /c dir";
    STARTUPINFOW si;
    PROCESS_INFORMATION pi;
    SECURITY_ATTRIBUTES sa;
    ZeroMemory(&si,  sizeof(STARTUPINFOW));
    ZeroMemory(&pi,  sizeof(PROCESS_INFORMATION));
    ZeroMemory(&sa,  sizeof(SECURITY_ATTRIBUTES));
    sa.nLength = sizeof(SECURITY_ATTRIBUTES);
    sa.bInheritHandle = TRUE;   
    sa.lpSecurityDescriptor = NULL;
    si.cb = sizeof(STARTUPINFOW);
    if (!CreateProcessW(NULL, (LPWSTR)buff, NULL,NULL,TRUE,CREATE_NO_WINDOW,NULL,NULL,&si,&pi)) // failed 
    {
        return GetLastError();
    }
    return 0;
}

If I use the ANSI functions and structs, this works fine, but when the W suffix is used, it does not work.