Resolving issues after cloning Virtual box virtual machine

Some times we may encounter few issues with cloned virtual machines at start up .

After cloning a linux Guest I tried to increase memory and started it but it is failed with an error message

Failed to open a session for the virtual machine

VT-x is not available.(VERR_VMX_NO_VMX).

Details

Result Code:
E_FAIL (0x80004005)
Component:
Console
Interface:
IConsole {8ab7c520-2442-4b66-8d74-4ff1e195d2b6}

I just changed RAM size back and started it then increased RAM (We need to shut down virtual machine to change it).

I think this issue can be fixed by also changing entries in vbox settings file , this file can be found in Virtualbox directory on host machine. We can open it with a text editor and make changes .

Cloned machine may not be able to start network interface at startup.My guest OS was showing just loopback interface after startup .
I just changed mac address of new cloned device to match with it’s own macadderss in file /etc/sysconfig/network-scripts/ifcfg-eth0 .
Network interface settings file location is different in other Linux distro for example ubuntu,debian will have network settings in /etc/network/interfaces file. I also changed mac address in /etc/udev/rules.d/70-persistent-net.rules ( we can find the macaddress from virtual machine settings—>Network) .