Sorry, no, I don't have a solution for your problem. DVDShrink has been giving more and more problems for people using faster systems and lots of ram. The program was written for Windows 98 and XP, and was abandoned in 2004, so hardware and software around it have changed dramatically.
It doesn't always know how to cope with buffering in a modern system, and there is no 64bit version. And its not an open software, so there will be no new versions even from other authors.
Here is a typical discussion of the program and out of memory issues with external drives: http://www.dvdshrink.org/forum/viewtopic.php?f=1&t=100609
I personally haven't experienced any problems, but I don't use external drives of any sort.