I'm not sure I understand the question you are asking.
Could you provide more information?
Here's what would be helpful:
[1] The version of alfresco that you're running
[2] The operating system that alfresco is on (e.g.: windows XP, Linux, etc..)
[3] The URL that appears to be returning nothing (the one in the empty window)
Also, if you see log messages from the virtualization server
when this occurs, please post them.