reactivation on starting Dreamweaver will normally happen if the Physical (MAC) Address for the active network card changes.
if you change between using a Wired and Wireless connection for example, this will change the MAC address since it is a different network card and case the need to reactivate.
It can also happen with some VPN clients that create a virtual network card where the virtual network card changes the MAC address frequently.
Do either of these scenarios fit you situation?
try this: before starting Dreamweaver, check the network settings and see what the mac address of the active netwrok card is. on windows, you can find this info by:
1) Go to the Start Menu -> Run. Type "cmd" and click on OK to bring up a command prompt.?
2) At the command prompt type "ipconfig /all"
make note of the active MAC address.
the next time you restart Dreamweaver, repeat this and compare the mac address with the one from the last time.