I'd suggest upgrading your ESXi to a newer patch revision. Seeing as you're not using vSphere, you probably haven't upgraded to newer patch revisions.
It's easy to do. See if it resolves this issue.
You're using VERY OLD builds of VMware. See this patch and revision chart. We can't even begin to troubleshoot your issues until you take care of your systems. 5.0.0 probably shouldn't even be used anymore, but 2000308 is the current build of 5.0.0. The 469512 build you're using is from 2011 and has been updated SEVENTEEN times...
Same thing for your 5.1.0 installation. The current revision for 5.1.0 is 2000251 instead of the 799733 you have.
For 5.5, you're using an unpatched build 1331820 - The current build is 1892794.
There are many bugs and issues that have been resolved over the years. So updating is a good thing to do.
/sbin/services.sh restart works for the moment, but I don't know that it's worth digging deeper when we know that the versions are so out-of-date.