Don't update VirtualBox to v4.3.18 or v4.3.20

If you have Windows 7 64bit, don't update VirtualBox to v4.3.18 or v4.3.20.  Most of your VMs won't start and instead you'll get an error message about can't load some DLL.  It's a known problem and no solution but going back to the prior version.  v4.3.12 Works fine.

I had to restore the system to make sure it's clean state and recover the VB.

Error: cannot retrieve metalink for repository epel. please verify its path and try again

I got that error message when I tried to use YUM on CentOS 6.

Two possible issues and solutions:

1. system time is incorrect.

2. ca-cert needs to be updated.

 

For #1, install NTP and set date/time:

1. yum install ntp npdate
2. chkconfig ntpd on
3. ntpdate pool.ntp.org
4. service ntpd start

For #2, update CA-cert: yum update -y ca-certificates