Doesn't anyone think that having one switch in RPVST mode with loopguard on and the other switch in PVST mode with no loopguard might contribute to this issue?

well as I said I took this from Cisco's own website.  I think it is a general rule and maybe there are circumstances where it does not work but it has helped me a great deal in remembering where and in what direction to apply the ACLs.http://www.cisc...

something great I found on a cisco forum somewhere that has always helped me to determine what direction is correct.The "in" ACL has a source on a segment of the interface to which it is applied and a destination off of any other interface. The "out"...