I believe this problem is caused by media sensing in Windows. It senses when various NIC cards are active or not and then turns off the inactive ones. This causes problems with Flexnet licensing. You need to turn off media sensing.
I suggest you download my talk from last year's PTC conference. You'll find it here:
http://portal.ptcuser.org/p/do/sd/sid=2464&type=0
The following is from that document.
Cheers - Dave Haigh.
(This is my first post to this site. You'll find me on the mail exploder. The only reason I replied to this is because someone linked to this in their question on that site. Not happy about it's coming demise.)
Media Sensing
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Add this registry setting:
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Tcpip\Parameters\
Name: DisableDHCPMediaSense
Data type: REG_DWORD (Boolean)
Value: 1
What the PTC folks were doing was just changing the order in which flexnet sees the NIC cards. Without turning off media sensing this isn't going to help. It will just change the next time Windows senses a different card is inactive.
Here's how to change the NIC sort order
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Expand the following key
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\NetworkCards
This key will contain numbered folders corresponding to all of the network cards installed on the machine
Locate the desired folder by matching the "Description" field in the Registry Editor to the "Description" line from the ipconfig /all output for the desired network card
Rename this folder to number 1
Close the registry editor
Restart the machine