Another person getting error 87

[microzen]

I've seen that other folks have had the same unsolved issue as me, namely:
I copied several client's sessions to a brand new external 2TB eSATA drive and they play fine. I can mix them all day without problem.
As soon as I do any overdub, no matter how large or small, ProTools can play the session up until the point where the new overdub was recorded, at which point it stops and gives the "error 87' message.
If I erase the overdub, the session is fine again, by which I mean it will play all the way through. I can once again make any mix changes I want, but I cannot record any new data to that session without getting the "error 87" at the point where the overdub starts.
Interestingly, I can copy any of these sessions to my older external 2.5" USB drive, which is only 5400 RPM and work on these same sessions, including recording overdubs without problems of any kind.
Yes, I can make and send you a Sandra report, but it seems there's only a problem recording new overdub data onto the eSata drive.
I've seen another person who posted the same issue; where the song plays fine until the overdub, at which point the 'error 87' appeared.
Any ideas?
Thanks in advance.