I have a 500Gb Western Digital HD WD5000AAJS (ZZYFA0) which keeps to suspend very frequently.
When I access it after a couple of minutes I need to wait for it to spin up again.
I'm using Win7 64bit, I disabled HD suspension, I tried to disable the head parking with WDIDLE but it told me that it was already disabled.
None of the solutions I tried, worked.
Regards.