Since upgrading to 10.11.4 my app store won't open.

Please test after taking each of the following steps that you haven't already tried. Stop when the problem is resolved. Back up all data before making any changes.

Sometimes the cause of the problem may be an outage in Apple's network, in which case none of the steps below will have any effect. You just have to wait for the outage to be fixed. That should rarely, if ever, take more than a few hours.

Step 1

Sign in to the App Store by selecting Sign In from the Store menu. If you're already signed in, sign out and then sign in again.

Step 2

Remove or disable "Little Snitch," or any similar third-party software that blocks outgoing network connections, according to the developer's instructions.

Step 3

From the menu bar, select

 ▹ System Preferences... ▹ Network

If the preference pane is locked, click the lock icon in the lower left corner and enter your password to unlock it. Then click the Advanced button and select the Proxies tab. If any proxy options are selected, make a note of them and then deselect them. You don’t need to change the bypass or FTP settings. Click OK and then Apply. Test. The result may be that you can't connect to any web server. Restore the previous settings if that happens.

Step 4

Log out or restart the computer.

Step 5

Start up in safe mode and log in to the account with the problem.

Note: If FileVault is enabled in OS X 10.9 or earlier, or if a firmware password is set, or if the startup volume is a software RAID, you can’t do this. Ask for further instructions.

Safe mode is much slower to start up and run than normal, with limited graphics performance, and some things won’t work at all, including sound output and Wi-Fi on certain models. The next normal startup may also be somewhat slow.

The login screen appears even if you usually login automatically. You must know your login password in order to log in. If you’ve forgotten the password, you will need to reset it before you begin.

After testing, restart as usual (not in safe mode.)

Step 6

If possible, connect to a different network and test.

Step 7

Reset the NVRAM.

Hi Linc and elvag...,

Thank you for your detailed post, however...., I have followed instructions carefully twice over as well as attempted "elvag's" solution but none of these seem to be working for me.

I do have Kaspersky Internet security installed but, even if I turn the av off...., I'm still unable to sign into my app-store in order to run advertised updates nor search any apps.

Do you have any other advice in order to get this resolved?

Your assistance are appreciated.