In the library
right click on windows 7 x64 and windows 7 x64 2 virtual machines and choose get info .
Compare the sizes of both entries
The one with least size ( usually it will be less than 50 MB ) is the one which you can safely remove.
To remove the invalid entry just right lick ( control + click ) on the least sized virtual machine and choose delete and choose move to trash.
Before emtying the trash just ensure to start your vm and make sure its running fine.
If you do not get any errors you may safely go ahead empty the trash.
Important : If the sizes of both virtual machines are greater than 2 GB, please send the support logs to have a better understanding of the scenario .
Click on help > collect support information.
This will create a tgz file on your desktop. Send it as attachment in your next reply
