Unable To convert .vmx to .ovf

HI

I got Workstation 7.1.5

I want to migrate my VM on to Esxi5.5

I tried to convert .vmx to .ovf with Command (ovftool E:\VM\VM4\VM4.vmx E:\OVF\OVF4\VM4.ovf)

But its failing with error :

C:\Program Files\VMware\VMware OVF Tool>ovftool E:\VM\VM4\VM4.vmx E:\OVF\OVF4\VM

4.ovf

Opening VMX source: E:\VM\VM4\VM4.vmx

Error: Failed to open disk: Windows Server 2008 x64-cl2.vmdk

Completed with errors