Using Dynamic DNS Host Name in Traffic Rule

New to the forum; hoping I can get some help.  I'm trying to set up remote desk top for my server - using Norton Smart Firewall to limit traffic on the remote port (3389) to just my own PCs.  To do this I:  1) Created an allow "specific computer" rule on the port (with highest precedence).   2) Created an allow "local subet" on the port  and  3) Created a "Block All" rule on the port (lowest precedence).  Rules #2 and #3 are working fine - I'm having problem with #1 - the specific computer.  I'm trying to use a DDNS host name managed by no-ip for my remote PC.  I enter the host name in the traffic rule and the first time it works.  I can see in the log  that the remote host and IP address are populated correctly.  If I try to connect a second time, it fails. From the log (Block All rule), I now see that the remote IP is still populated but the remote host is blank - thus the reason that Rule #1 did not fire.  If I delete the Rule and add it back - I get the same thing - one time success and then failure. Does anyone have any thoughts as to what could be going on - and what a remedy might be?
Thanks.