Using an SCR is going to give you even more trouble.If it works well without a load then it is switching that load that will give you the interference which I assume is what you mean by trouble.So what are you switching?Try some snubber circuits on it. Add a capacitor across the low voltage power supply on your relay board.If it does not cover the arduino and plug into it, then it is not a shield it is just a board.Yes I mean a simple blink type program.
So it looks like your load is interfering with your web server. Again tidy up the wiring and put extra decoupling on external circuitry.
problem is with my sketch
But you said that without a load on the relay then your sketch worked. If this is true then no ammount of software is going to change things.Are you now saying it didn't work without a mains load on the relay?
What kind of mystery is that?
No kind of mystery at all.Interference spikes are produced on the load turning on and off. The spikes are not bad enough to crash the arduino every time but they are big enough for there to be a probability of crashing it. Therefore by rapidly turning it on and off you give it more chances of crashing.I believe you have been told enough times how to cure this.
How to cure that ?
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OK I must try adding capacitors to my relay board but can u tell me where should I add it?
I didn't got you by isolated strips?