Not real memory in VPS

Hi, I have my 3th DNSONLY server in Host1plus.com VPS with 512MB of RAM and I get memory errors when it should have most of the memory available.

Look here: http://ift.tt/1smvPNR

And here: http://ift.tt/12AcPqr

I should say that's an overselling issue, there's no real memory for the VPS instances, right ?

http://ift.tt/1dvHQ0Z