I had a same issue, i am able to view VM console from vcenter server, i installed vsphere client on my desktop and i used same vcenter credentials, but i couldn't see VM console, showing same error unable to connect to the MKS: internal error.
finally i found the error is with DNS. Name resolution is not happening. Use nslookup command and check proper DNS connectivity, and also do following changes from this site http://www.gkhan.in/mks-internal-error-on-vmware-console/