Code on sunny boy

[lj.l]

Has anyone ever had code 6403 on a sunny boy 3680 inverter. The inverter has been replaced 3 times on advice from SMA as they are saying it's an internal component failure, surely not on 4 inverters though.
The original install was done by myself in February and all was fine until a few weeks ago. I have retested all the AC & DC ,had the DNO out and everything is as it should be. It's back in SMAs hands now but no one can offer a solution.

 

[Worcester]

The only time we've had multiple failures it was definitely the DNO's fault, despite and initial denial AND installing a dataloggger, which they said showed no problems, they then replaced 2km of overheads that had about 20 joints in it from multiple line failures, and voila, now we have no more failed inverters...

- They didn't admit to us that they had replaced the overheads, it was the homeowner that let us know it was going on!