I have a VM that I can't add memory to, hot plug is enabled but the section to add memory is grayed out. This is a windows server 2008 R2 64 bit, VM version 9, the VM is running and I can't power it off during the day. I migrated it to another host but that didn't help, I successfully added memory to 3 other VMs with the same configuration. Any ideas on what is wrong?
I was looking into this thread yesterday when my ADSL modem failed. 
Sorry I didn't get back to you sooner.
Is there any chance that the virtual machine started off with 2 GBytes of RAM when it was previously powered on, and then hot-added all the way up to 32 GBytes? We have a "maximum growth" factor which defaults to 16; With a VM with 2 GBytes at power-on, the maximum grow factor would limit the VM to 32 GBytes of RAM. We found that limiting the growth in this way avoids issues with many guest OSes which don't expect such dramatic changes in memory capacity... most physical hotplug systems will see a maximum realistic growth of 2 or 4 or perhaps 8 times, and many OSes implicitly assume such a limit.
The other possibility is that you may have run out of memory hotplug "slots"... We need to provide some faked-out description of the system's "memory modules" to the guest OS, and our platform has an upper limit of 512 such "slots" to describe the hotpluggable memory. Particularly if you have memory hot-remove enabled or if you are using virtual NUMA, a hot-add of memory might use a surprisingly large number of those "slots", which could lead to an inability to add more memory later.
The vmware-*.log from the VM's previous run might help verify if one of the above explanations is the cause, or it might contain some more clues to help understand what happened.
Thanks,
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Darius