Mac says unknown error when i try to download yosemite

Question

when i try to download iOS yosemite onto my mac it says unknown error and then won't continue. my mac is the macbook pro retina display the thin version. i have 162 GB free of flash storage and says i have an 8GB memory. the last version of iOS mavericks is installed on it 10.9.5 so I'm sure its able to do it. I've tried going on different internet. and still the same thing. i also have a iMac desktop the newest one and it also says the same exact thing. can someone please help me

Answer 1

Give this a try:
Repair the Hard Drive and Permissions - Yosemite, Mavericks, Mountain Lion or Lion
Boot to the Recovery HD:
Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.
Repair
When the recovery menu appears select Disk Utility. After DU loads select your hard drive entry (mfgr.'s ID and drive size) from the the left side list.  In the DU status area you will see an entry for the S.M.A.R.T. status of the hard drive.  If it does not say "Verified" then the hard drive is failing or failed. (SMART status is not reported on external Firewire or USB drives.) If the drive is "Verified" then select your OS X volume from the list on the left (sub-entry below the drive entry,) click on the First Aid tab, then click on the Repair Disk button. If DU reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported then click on the Repair Permissions button. When the process is completed, then quit DU and return to the main menu. Select Restart from the Apple menu.