The VMWARE vSphere client closes or crashes when you right click on a host and select Import Machine.
You probably have an older version of the VMWARE client such as VI Client 2.5 installed for administration of older ESX installations.
There is a DLL conflict documented in http://www.vmware.com/support/vsphere4/doc/vsp_vcc_41_rel_notes.html, although it describes a Visual C++ Runtime error which I did not receive.
The solution documented in the release notes works though which is to remove (although I suggest rename) the following files located in C:\Program Files\VMware\Infrastructure\Virtual Infrastructure Client\Launcher:-
Once renamed/removed if you have the vSphere client open, close the client and open it again otherwise simply open the vSphere client. The vConverter utility should now run when you use Import Machine.