The "ERR" message could be the result of many malfunctions in the camera. For example on a F100 I would get ERR because the self check on the shutter indicated the shutter time was out of spec. It had nothing to do with the electronics but was telling me the shutter needed service or replacement. Releasing the shutter or cycling power would clear the error for a while. I'm sure there are several such self checks made in current DSLRs.
I surprised that Nikon replaced the computer. It seems to me that it is more likely the computer is working correctly and telling you that some other part is not working properly. If you can do long bursts at 7fps, the the computer is working fine up to the point you get "ERR". Computers are unlikely to have failures that behave like that.
Does an additional shutter release or power off/on cycle clear the problem for a while?
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