Hmm, it should still work with NT4. It sounds like an incompatibility with some other program installed on your box (although if the previous version works, it's not too likely as there've been very just a very few changes in the file system filter driver that may be causing this).
The sad thing is that NT4 has so limited debugging capabilities. If it was at least Win2K, I'd tell you to generate a dump file for me; but in the case of NT4, I'm a bit unsure how to find out what's causing the problem...
One thing: does the problem happen if you don't install the Standard, IM and P2P Shields? (i.e. select "Custom" during installation, and uncheck these three checkboxes).
Thanks
Vlk