Memory upgrade - stuck at loading scheduler

I am trying to upgrade the RAM memory on my ESXi 5.1 host licensed with the essentials kit.

Currently the host has 32 Gb memory. If I insert an additional 32, bringing it to 64 Gb, the OS reboots itsself during the step "initializing scheduler".

I cannot seem to find info stating that the essentials license comes with a 32 Gb limitation. Anybody knows if it does or not?

If it is not license related, we will look into hiring someone to have a look at the problem but just want to make sure it is not a license issue.

Thanks for your reply.