From your description I don't think Copy Protection is causing your problem and since you're recording directly to HDD it eliminates most problems with the DVD drive.
It's got me stumped unless you're having some type of power or power supply problem. By power I mean from your power company, low or dropping power levels, overloaded circuit in your house, etc. By power supply I mean the EH-55's internal power supply/capacitors etc. which can cause problems but I don't think exactly like yours.
If it were me I'd try experimenting with recording directly to DVD instead of the HDD(maybe you're HDD is fragmented?) or trying to figure what else is on the same circuit(circuit breaker/fuse) as your EH. You don't want anything like a larger heater or something with a compressor or motor which could possibly cause a power drop resulting in odd happenings.
Just stabbing in the dark but it's what I'd try first, Good luck.