Not able launch my ubuntu guest after upgrading virtual box

[Saicharan]

I upgraded my virtual box on windows host to 4.2.4. Now i am having problems starting my linux guest. Getting the following error.

Failed to open a session for the virtual machine Ubuntu.

VT-x features locked or unavailable in MSR. (VERR_VMX_MSR_LOCKED_OR_DISABLED).

Result Code: E_FAIL (0x80004005)
Component: Console
Interface: IConsole {db7ab4ca-2a3f-4183-9243-c1208da92392}

Please help.

I then disabled hardware acceleration. Then ubuntu guest os starts but in the middle of the boot it says fatal error, going into guru meditation mode.
I have attached the log also.

Please help all my work is in the ubuntu guest os.

[mpack]

You must have updated something else besides VirtualBox.

VMX_LOCKED_OR_DISABLED means that something else is already using VT-x. Typically this would be another VM platform, or sometimes the debug driver for a development environment. Only you can know.

Disabling VT-x in the VM recipe is only viable if the guest does not require VT-x. E.g. VT-x is required to run 64bit guests.

[Saicharan]

I had allocated 4gb of my ram to the guest OS.
That was the problem.
Reduced it to 3.5gb now its working.
Thanks