Error { }

Está faltando algum } aqui?

This missing close some } here?

//COMANDOS WEB
EthernetClient client = server.available();
if (client) {
boolean currentLineIsBlank = true;
String str;
while (client.connected()) {
if (client.available()) {
char c = client.read();
str.concat(c);}

if(str.endsWith("/1on"))
{BOTAO1_RELE =1;}
else if(str.endsWith("/1off"))
{BOTAO1_RELE =0;}

if (c == '\n' && currentLineIsBlank) {
client.println("HTTP/1.1 200 OK");
client.println("Content-Type: text/html");
client.println();
}

If you put each { and } on its own line then Auto Format the code (Ctrl/T) then it becomes obvious that there is no closing brace on

if (client)

and

 while (client.connected())

At least not in the snippet of code that you posted.