Today I had to reinstall another OS X on a MacBook pro and I was using the same installation USB flash drive created as showed in the previous post and today I got the message "This copy of the install OS X El Capitan application can't be verified".
After some research I found the following fix.
It seams that the problem was with the date. So, before you start installing the OS X, open terminal and type "date MMDDHHmmYY" where
MM - 2 digit month 01 - 12
DD - 2 digit date 01 - 31
HH - 2 digit hour 01 - 24
mm - 2 digit minute 01 - 59
YY - 2 digit year > 15This fixed my problem and I was able to install OS X El capitan.