First, click your download link again to get the current 2.517 version, or wait a few more days to get the new 2.518 we will start testing today. There are many bugs fixed and features added between 2.506 and 2.517. You don't want to reinstall 2.506.
Second, I don't know why, but your registration code had been disabled. I find no reason for this in our records, so I have enabled it. You should now be able to install 2.517 or 2.518 on either of of your 2 computers.

Sorry gduns, you confused Microstudio with KHP. Microstudio does not use the MACID of a network card.