magento2: Magento 2.0.4 running painfully slow on Wamp, unable to load pages or save settings: Error: client denied by server configuration app/etc/config.php

Steps to reproduce

1. Installed Magento 2.0.4 on WAMP 3.0 on windows 10 Pro 32 bit, 4 GB Ram, PHP 5.6.15, My SQL 5.7.9, Apache 2.4.17. My localhost base url is: http://127.0.0.1:8080/mymagento/
2. The new magento installation worked fine for few days, But now suddenly it became too slow… Not able to load pages in frontend and unable to save settings in admin too. Browser just keep waiting…
3. Checked apache error log… These errors are coming every time I am refreshing my localhost url…

[access_compat:error] [pid 14060:tid 964] [client 127.0.0.1:57098] AH01797: client denied by server configuration: E:/wamp/www/mymagento/app/etc/config.php
[access_compat:error] [pid 2336:tid 1088] [client 127.0.0.1:57101] AH01797: client denied by server configuration: E:/wamp/www/mymagento/app/etc/config.php

1. Already cleared var and pub/static folders, restarted wamp several times. Also, ran commands

php bin/magento indexer:reindex
php bin/magento setup:upgrade
php bin/magento maintenance:disable

1. In fact this issue came after I ran command php bin/magento setup:upgrade last time, although I have used this command earlier too with no issues. So, not confirm this is the cause.

Note: Much time earlier when I ran php bin/magento setup:static-content:deploy command on a separate magento 2 installation this (painfully slow) issue came and I had to reinstall this magento when no other solution found. For the same fear, I am also not enabling merge css/js setting in magento admin this time (which I did in old installation, suspecting it a cause #3651 )

Note 2: I don’t think this is php memory_limit or execution_time issue. bcoz I have already increased it sufficient, and was working fine on these settings until this slowness issue appeared. Further, I have already set few (not all) settings as per guide http://www.devside.net/wamp-server/wamp-is-running-very-slow to optimize the WAMP & mysql performance.

Actual result

Painfully slow, without a identifiable reason. Unable to load pages in frontend and unable to save settings in admin too. Browser just keep waiting. (Although I have found, occasionally it runs well sometime. Weird!)

Any solution?

Thanks.